: EHE A ERHEBEN ENGEN, ss MOINE HE a Alls bd i if 7 4; f in ‘aa 1 fiat # I BE e i een er) ie TE, HI KE 4 4 ; H ñ A i ; - ACTE G PEST ers Seats eet es 3; Re RARES are bie ur ; pri i oe NON =) | Bar LE Fr rl jie - tal wd vr 1 Paleontological Research QE ISSN 1342-8144 Formerly Transactions and Proceedings of the Palaeontological Society of Japan Vol. 3 No.1 April 1999 The Palaeontological Society of Japan ; Co-Editors Kazushige Tanabe and Tomoki Kase Language Editor Martin Janal (New York, USA) Associate Editors Jan Bergström (Swedish Museum of Natural History, Stockholm, Sweden), Alan G. Beu (Institute of Geological and Nuclear Sciences, Lower Hutt, New Zealand), Satoru Chiba (Tohoku University, Sendai, Japan), Yoichi Ezaki (Osaka City University, Osaka, Japan), James C. Ingle, Jr. (Stanford University, Stanford, USA), Kunio Kaiho (Tohoku University, Sendai, Japan), Susan M. Kidwell (University of Chicago, Chicago, USA), Hiroshi Kitazato (Shizuoka University, Shizuoka, Japan), Naoki Kohno (National Science Museum, Tokyo, Japan), Neil H. Landman (Amemican Museum of Natural History, New York, USA), Haruyoshi Maeda (Kyoto University, Kyoto, Japan), Atsushi Matsuoka (Niigata University, Niigata, Japan), Rihito Morita (Natural History Museum and Institute, Chiba, Japan), Harufumi Nishida (Chuo University, Tokyo, Japan), Kenshiro Ogasawara (University of Tsukuba, Tsukuba, Japan), Tatsuo Oji (University of Tokyo, Tokyo, Japan), Andrew B. Smith (Natural History Museum, London, Great Britain), Roger D.K. Thomas (Franklin and Marshall College, Lancaster, USA), Katsumi Ueno (Fukuoka University, Fukuoka, Japan), Wang Hongzhen (China University of Geosciences, Beijing, China), Yang Seong Young (Kyungpook National University, Taegu, Korea) Officers for 1999-2000 President : Kei Mori Councillors : Kiyotaka Chinzei, Takashi Hamada, Yoshikazu Hasegawa, ltaru Hayami, Hiromichi Hirano, Noriyuki Ikeya, Junji Itoigawa, Tomoki Kase, Hiroshi Kitazato, Itaru Koizumi, Haruyoshi Maeda, Ryuichi Majima, Makoto Manabe, Hiroshi Noda, Ikuo Obata, Kenshiro Ogasawara, Terufumi Ohno, Tatsuo Oji, Tomowo Ozawa, Yukimitsu Tomida, Tsunemasa Saito, Takeshi Setoguchi, Kazushige Tanabe, Akira Yao Members of Standing Committee : Hiroshi Kitazato (General Affairs), Tatsuo Oji (Laison Officer), Makoto Manabe (Finance), Kazushige Tanabe (Editor in Chief, PR), Tomoki Kase (Co-Editor, PR), Ryuichi Majima (Planning), Hiromichi Hirano (Membership), Kenshiro Ogasawara (Foreign Affairs), Haruyoshi Maeda (Publicity Officer), Noriyuki Ikeya (Editor, “Fossils”), Yukimitsu Tomida (Editor in Chief, Special Papers), Tamiko Ohana (Representative, Union of Natural History Societies), Secretaries : Masanori Shimamoto, Takao Ubukata (General Affairs), Hajime Taru (Planning), Tokuji Mitsugi (Membership), Shuko Adachi (Foreign Affairs), Kazuyoshi Endo, Yasunari Shigeta (Editors of PR), Akira Tsukagoshi (Editor of “Fossils”), Naoki Kohno (Editor of Special Papers) Auditor : Nobuhiro Kotake Notice about photocopying: In order to photocopy any work from this publication, you or your organization must obtain permission from the following organization which has been delegated for copyright for clearance by the copyright owner of this publication. Except in the USA, Japan Academic Association for Copyright Clearance (JAACC), 41-6 Akasaka 9-chome, Minato-ku, Tokyo 107-0052, Japan. Phone: 81-3-3475-5618, Fax: 81-3-3475-5619, E-mail: kammori @msh.biglobe.ac.jp In the USA, Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA. Phone : (978) 750-8400, Fax : (978)750-4744, www.copyright.com Cover : Idealized sketch of Nipponites mirabilis Yabe, a Late Cretaceous (Turonian) nostoceratid ammonite. Various reconstructions of the mode of life of this species have been proposed, because of its curiously meandering shell form (after T. Okamoto, 1988). All communication relating to this journal should be addressed to the PALAEONTOLOGICAL SOCIETY OF JAPAN c/o Business Center for Academic Societies, Honkomagome 5-16-9, Bunkyo-ku, Tokyo 113-8622, Japan Paleontological Research, vol. 3, no. 1, pp. 1-17, 6 Figs., April 30, 1999 © by the Palaeontological Society of Japan Permian bivalves from West Spitsbergen, Svalbard Islands, Norway KEWUI NAKAZAWA 28-2, Koyama Shimouchikawara-cho, Kita-ku, Kyoto 603-8132, Japan Received 6 June 1998; Revised manuscript accepted 27 December 1998 Abstract. The bivalve fossils collected by Japanese-Norwegian research groups from the Kapp Starostin Formation in west Spitsbergen are described. They comprise fourteen species belonging to the Pterioida and two species of the Arcoida. Among them, six species, including two that are indeterminate, are newly described. They are Grammatodon (Cosmetodon) ? suzuki, G. (C.)? sp. ind., Streblochondria win- snesi, Vorkutopecten svalbardensis, Deltopecten sp. ind., and Palaeolima nakamurai. The fauna belongs to the Boreal bioprovince, but a single species, Cassianoides sexcostatus (Stuckenberg) has also been reported from the Central Rocky Mountains of the United States. The bivalve fauna suggests an Artinskian-Kungurian age for the Kapp Starostin Formation. This is somewhat earlier than the age deduced from brachiopods and bryozoans, but it is not decisive because the materials are poor. The Kapp Starostin Formation is conformably overlain by the Otoceras-bearing, earliest Triassic Vardebukta Formation, so a time-gap corresponding at least to the Dorashamian and Dzhulfian (= Tatarian) is inferred between the two formations. Key words: Kapp Starostin Formation, Permian bivalves, Spitsbergen Introduction The study materials were collected by Nakamura et al. in 1984 and 1990, and by Nakazawa et al. in 1986 from the Permian Kapp Starostin Formation of west Spitsbergen, in the Svalbard Islands, Norway. Brachiopods and bryozoans are most abundant among the macrofossils. Many species of brachiopods have been described by various authors, notably, Frebold (1937) and Gobbet (1963). Bivalves are found rather rarely and the descriptive studies are few. Toula (1873, 1875a, b) first described the following species, collected from “Carboniferous-Permian” strata on Sdérkapp Island off the southerntip of Spitsbergen, and Axel Island in Bellsund and on Hornsund, on the west coast of Spitsber- gen: Pecten (Aviculopecten) bouei Verneuil, Pecten (Aviculopecten) kokscharofi Verneuil, Pecten (Aviculopecten) cf. ellipticus Phillips, Pecten (Aviculopecten) cf. dissimilis Fleming, Pecten (Aviculopecten) wilczeki Toula, Gervillia cf. antiqua Münster, Aviculopecten draschei Toula and Gervillia sp. Frebold (1937) described the following species, mostly from the upper part of the Kapp Starostin Formation in the Festningen section, located on the southern coast of Spits- bergen at the entrance to Isfjorden and from Sorkapp Island : Aviculopecten (Deltopecten) cf. mutabilis Licharew and A. (D.) cf. hiemalis Salter, Aviculopecten? sp. indet., Pecten (Aequipecten) ? keyserlingiformis Licharew, Pecten (Aequi- pecten) keyserlingi Stuckenberg, Pecten (Pseudamusium) cf. ufaensis Tschernyschew, Pecten (Pseudamusium) ex aff. sericeus Verneuil, Parallelodon sp. ind, genus | =Paral- lelodon ?] et sp. ind., Clidophorus ? sp. ind., Pecten wilc- zeki Toula, and Leda sp. ind. Among the species described by Toula, Aviculopecten bouei was referred to Aviculopecten (Deltopecten) mutabilis by Licharew (1927). Pecten cf. ellipticus was identified as Pecten (Pseudamusium) ex aff. sericeus Verneuil, and Pecten (Aviculopecten) cf. dissimilis was compared to Aviculopecten netschajewi Licharew and reported as Aviculopecten ? sp. ind. by Frebold (1937). Aviculopecten kokscharofi reported by Toula (1873) is probably identical with Aviculopecten cf. hiemalis illustrated by Licharew (1927, especially pl. 5, fig. 20), and is referred to Etheripecten cf. mutabilis Licharew in the present paper. Among the species reported by Frebold, Aequipecten keyserlingi was considered to belong to the genus Mor- rispecten Muromtseva and Guskov by Muromtseva (1984, p. 75). Morrispecten is, however, a junior synonym of Undo- pecten Waterhouse, 1982 (Newell and Boyd, 1995). Pecten (Aequipecten) ? keyserlingiformis and Aviculopecten (Deltopecten) cf. mutabilis and A. (D.) cf. hiemalis of Frebold are referred to Etheripecten keyserlingiformis and E. ci. mutabilis ?, respectively. Pseudamusium cf. ufaensis and Parallelodon sp. ind. are identified as Streblochondria win- snesi sp. nov. and Grammatodon (Cosmetodon) ? suzuki sp. i) nov., respectively, in the present paper. Sixteen species including four new species and two indeterminable ones are described. All the materials are kept at the Department of Geology and Mineralogy, Faculty of Science, Kyoto Univer- sity. Stratigraphy The fossils were collected at four localities in west Spits- bergen, namely, the Festningen section along the southern coast of the entrance to Isfjorden, the Skansbukta section at Billfiorden, and the Reinodden and Ahlstrandodden sections along the southern coast near the entrance of Van Keulenf- jorden, in Bellsund (Figure 1). Faunas from the first and second localities were collected on Nakamura’s expedition in 1984 and in 1990. The stratigraphy of these sections was published by Nakamura et al. in 1990 and, in more detail, by the Japanese-Norwegian Research Group (1992). The other two localities were examined by Nakazawa's party in 1986 and the results were published by Nakazawa et al. (1990). All the materials are from the Permian Kapp Staros- tin Formation which was defined by Cutbill and Challinor (1965). The formation corresponds to the Brachiopod Cherts (including the Spirifer Limestone at the base) of previous authors (e.g., Gee et al., 1953). At the type locality, Festnin- gen, the formation is divided into three members, the Vo- ringen, Svenskeegga, and Hovtinden Members in ascending order (Cutbill and Challinor, 1965). (1) Festningen section (Figure 2A) At Festningen the Kapp Starostin Formation is 385 m in thickness and divided into twelve units (Nakamura et al. 1990 ; Japanese-Norwegian Research Group, 1992). Unit 1, about 20 m thick, is represented by brachiopod-rich, bioclas- tic limestone beds corresponding to the Voringen Member. Units 2 to 5, about 140 m thick, constitute the Svenskeegga Member, each represented mainly by siliceous shale, spicularite, spicularite and shale, and bioclastic limestone, respectively. rt D Ay rms for \>2°___/ Longyearbyen Bellsund \~_ En A Hornsund ~ 2 Figure 1. Map of southern Spitsbergen showing fossil localities. a: Skansbukta, b: Festningen, c: Reinodden, d: Ahlstrandodden. Keiji Nakazawa The Hovtinden Member, about 225 m thick, consists of seven units, 6 to 12, each composed mainly of spicularite, alternation of spicularite and spicularitic shale, bioclastic limestone, spicularite, bioclastic limestone (partly silicified), alternation of siltstone and paper shales, and quartzose sandy shale or siltstone, respectively, in ascending order. Bivalve fossils have been obtained from Units 5, 7, 8,9 and ats (2) Reinodden section (Figure 2B) At Reinodden the formation reaches more than 300 m in thickness. It is classified into eight units, A to H, in ascend- ing order (Nakazawa et al., 1990). Unit A, less than 5m thick, is the Voringen Member consisting of fossiliferous bioclastic limestone. Units B and C are referred to the Svenskeegga Member. Unit B, about 40 m thick, is sub- divided into three beds or subunits, 2 to 4. Beds 2 and 4 are represented by nodular or irregularly bedded, alternating spicularitic chert and thin mudstone. Bed3 consists of black laminated shale and siltstone. Unit C, about 80m thick, includes bedded black shale (Bed 5), and alternations of calcareous sandstone and limestone (Beds 6 and 7). The Hovtinden Member (Units D to H), about 180 m thick, is characterized by coarse-grained sandstone and spicula- rite. It is subdivided into fourteen beds, Beds 8 to 21, as shown in Figure 2B. Glauconite is commonly found in the sandstones. Macrofossils have been collected from ten horizons (RP 1~10) in the Kapp Starostin Formation, among which RP 3, 7 and 9 contain bivalve fossils. (3) Ahlstrandodden section (Figure 2C) At Ahlstrandodden the formation is about 250 m thick. It is divided into eight units, 1 to 8 (Nakazawa et al., 1990). Unit1, 7.6m thick, consists of brachiopod-rich bioclastic wackestone of the Voringen Member. Units 2 and 3, which are 40 m and 58 m thick, respectively, are correlated to the Svenskeegga Member. Units4 to 8, about 140m thick altogether, correspond to the Hovtinden Member. They are composed mainly of spicularitic chert or spicularite, siliceous shale and a minor amount of limestone. Glauconite grains are commonly found in siliceous sandstones throughout the Hovtinden Member. Among nine fossiliferous horizons (AP 1~9) within the formation, five horizons, AP 1,2,6,7 and 8, yield bivalve shells. The fossiliferous horizons AP 8 and 9 of the upper part of the Hovtinden Member can be correlated with hori- zons RP 9 and 10 in the Reinodden section. They are considered to correspond to horizon F 8 of the Festningen section. Fossil occurrence and age assignment Sixteen species in nine genera are identified from three sections mentioned above, plus one species, Acanthopecten licharewi (Fredericks), from Skansbukta (SA 7), as shown in Figures 3. The localities and stratigraphic horizons are shown in Figure 2. Nakamura et al. (1987, 1992) distinguished five brachiopod assemblage zones in the Kapp Starostin Formation of the Isfiorden area. They compared these faunas to those of Russia, Arctic Canada, Greenland, and Alaska, all belonging Permian bivalves from West Spitsbergen 3 A, FESTNINGEN 400 350 ERS B. REINODDEN 300 250 & = = = > fo) [e] | = = 200 E [o} mw 150 Starostin Kapp Svenskeegga Member 100 on [=] Bi H FE —— MN Her 10 6 RP fees C, AHLSTRANDODDEN es (OF She D ID OO DIAOlODEIENO 1 AP 1(9,10) Figure 2. Geological columnar sections of the Kapp Starostin Formation at three localities showing horizons of macrofossils. a: chert or spicularite, b: shale or mudstone, b’: siliceous or spicularitic, c: sandstone, Cc’ : siliceous, d: limestone, d’: siliceous, e: dolostone, e’ : dolostone nodule, f: calcareous, g: muddy. Numbers in parentheses correspond to those of bivalve species in Figure3. A: simplified from Japanese-Norwegian Research Group (1992, fig. 2), B and C: from Nakazawa et al. (1990, fig. 2). to the Boreal bioprovince. From the correlation of these faunas, they concluded that the Kapp Starostin Formation ranges in age from Kungurian up to Midian or early Dzhulfian (Tatarian). Sakagami (1992) studied the bryozoans and pointed out the similarity of the fauna from the Voringen Member with the Kungurian fauna in the Timan-Pechora region. Faunas of the Svenskeegga and Hovtinden Mem- bers resemble Ufimian faunas of Arctic Canada and the Russian Far East, the Kazanian fauna of the southern Urals, and the Late Permian fauna of British Columbia. These comparisons are consistent with the age range inferred from the brachiopods, except that there is no positive evidence, from the bryozoans, of the presence of Dzhulfian strata. These observations support previous views on the age of the Kapp Starostin Formation, for example, Forbes et al. (1958) and Flood et al. (1971). The ranges of the bivalve species are shown in Figure 3. Only two species, Vorkutopecten svalbardensis and V. aff. svalbardensis have been found in the Voringen Member. The overlying Svenskeegga Member is also poor in bivalves. Five species have been collected there, namely, Ether- ipecten cf. mutabilis, Etheripecten wilczeki, Vorkutopecten svalbardensis, Acanthopecten licharewi, and Deltopecten sp. All infrequently occur and their ranges extend up into the Hovtinden Member. Accordingly, the fauna is not essen- tially different from that of the Hovtinden Member. Eight and ten species could be identified from the lower and upper parts of the Hovtinden Member, respectively. In addition to species ranging up from the Svenskeegga Member, Streblopteria cf. eichwaldi, Streblopteria ? sp. and Palaeolima nakamurai appear from the lower part, but they have not been found from the upper part. The upper part is relatively rich in bivalve fossils. Grammatodon (Cos- metodon) ? suzukii, G. (C.) ? sp., Etheripecten keyserlingi- formis, E. aff. sichuanensis, E.? alatus, Streblochondria winsnesi and Cassianoides sexcostatus appear here. The intimate relationship of the Spitsbergen fauna with that of the Russian Arctic region (Ural, Pechora, Russian Platform, Verkhoyansk) is shown by the occurrence of the following species : ety . Grammatodon (Cosmetodon)? sp. ind. . Acanthopecten licharewt (Fredericks) . Etheripecten cf. mutabilis (Licharew) . Etheripecten wilezeki (Toula) Vorkutopecten svalbardensts sp. nov. 2 3 4 5 6. a 8. 9% 0. 1 Rone . Streblochondria winsnest sp. nov. wo . Deltopecten sp. ind. PAs wn . Streblopteria? sp. ind. N a . Palaeolima nakamurat sp. nov. Figure 3. Compiled range-chart of bivalve fossils. Skansbukta. Acanthopecten licharewi (Asselian-Artinskian of the Urals, Kungurian of Pechora, Lower Permian of Verkhoyansk), Etheripecten keyserlingiformis (Upper Carboniferous ?-Lower Permian of the Urals and Pechora), E. cf. mutabilis (Upper Carboniferous-Lower Permian of the Urals, Timan, Siberia), E.? alatus (Lower Permian of Pai Khoi in Siberia), Streblopteria cf. eichwaldi (Artinskian of the Urals and Russian Platform), and Cassianoides sexcostatus (Artinskian of the Urals and Russian Platform). Cassianoides sexcostatus is also report- ed from the Guadalupian of the United States (Branson, 1930 ; Ciriacks, 1963) and Etheripecten sichuanensis occurs in the Upper Permian of South China (Cheng et al., 1974). The stratigraphic occurrences of these species suggest that the Kapp Starostin Formation ranges in age from Artinskian to Kungurian. This is somewhat earlier than the age range inferred from the brachiopods and bryozoans, but the materials are poor and the conclusion is not definitive. The Kapp Starostin Formation is conformably overlain by the Lower Triassic Vardebukta Formation of the Sassendalen Group (Nakazawa et al., 1990 ; Nakamura et al., 1990). The earliest Triassic age of the basal part of this formation is indicated by the occurrence of Otoceras boreale Spath together with Claraia stachei (Bittner) (Kortshinskaya, 1986 ; Nakazawa et al., 1987). Hence, a time-gap corresponding at least to Dzhulfian-Dorashamian ages is indicated between the Permian and the Triassic beds. . Cassianoides sexcostatus (Stuckenberg) *: Festningen, Keiji Nakazawa Hovtinden Svenkeegga Member Member Vèringen . Grammatodon (Cosmetodon)? suzukii sp. nov. . Etheripecten keyserlingiformis (Licharew) Ethertpecten aff. sichuanensis (Chen et al.) Etheripecten? cf. alatus (Lyutkevich and Lobanova) Vorkutopecten aff. svalbardensis sp. nov. . Streblopterta cf. eichwaldi (Stuckenberg) “: Reinodden, *: Ahlstrandodden, ~ : Acknowledgments | am very grateful to T.S. Winsnes, formerly of the Norsk Polarinstitutt, for his critical reading of the manuscript. V. Kotlyar (VSEGEI) and B.A. Muromtseva (VNIGRI) in Russia, T. Ishibashi of Kyushu University, and J. Tazawa of Niigata University, Japan gave me useful information and valuable references to the literature. K.Nakamura of Hokkaido University kindly made his collection available for study. H. Suzuki of Doshisha University, F. Kumon of Shinshu Univer- sity and E.H. Siggerud from Norway cooperated with me in the field. T.Setoguchi, F. Masuda, and T.lrino of Kyoto University made various facilities available for preparation of the manuscript. | wish to thank all these people very much. Systematic description Order Arcoida Stoliczka, 1871 Family Parallelodontidae Dall, 1890 Subfamily Grammatodontinae Branson, 1942 Genus Grammatodon Meek and Hayden, 1861 Subgenus Cosmetodon Branson, 1942 Grammatodon (Cosmetodon) ? suzukii sp. nov. Figures 4-1a, b Parallelodon sp. ind. Frebold, 1937, p. 55, pl. 1, figs. 8, 9. Materials —A pair of left and right external molds. Permian bivalves from West Spitsbergen Holotype, Reg. no. HP 100050. Etymology.—Dedicated to Dr. Hiroyuki Suzuki of Doshisha University, who worked in the field with the author. Diagnosis.—Permian Grammatodon characterized by well developed, fine radial ribs and a little arcuate ventral margin. Description.—Shell moderate in size, a little inflated, elon- gated subquadrate with subparallel dorsal and ventral mar- gins, rounded anterior and truncated posterior margins ; ventral margin slightly arcuate ; 41 mm long and 19 mm high ; umbo broad and low, raised above the hinge margin, situated at anterior one-fifth of shell length ; bluntly rounded umbonal ridge running from the umbo to the posteroventral extremity ; surface covered by numerous, weak radial striae, wider than the interstices, approximately fifteen per centimetre width on the medial surface of the shell, one centimetre from the umbo ; densely spaced concentric growth lines form cancel- late sculpture with the radials (Figure 4-1b) ; hinge and inter- nal characters not observable. Comparison.—Two incomplete specimens illustrated by Frebold (1937) from near the same horizon at Festung (= Festningen) are identical with the present species. Based on Permian material from Malaysia, Yancey (1985) pointed out the possibility that most of the Paleozoic species de- scribed as Parallelodon should be referred to Grammatodon (Cosmetodon). Although the present species does not show its hinge characters, it is identified with that genus on the basis of its external shape and ornament. It is similar to the Guadalupian Cosmetodon multistriatus (Girty, 1908, p. 423, pl. 31, figs. 13, 14) in its shape and weak radial ornament, but it differs from that species in having less numerous radial striae, a little arcuate ventral margin and a larger size. Occurrence.—Rare in black shale of the uppermost fossil horizon, in the Hovtinden Member (F11) at Festningen. Grammatodon (Cosmetodon) ? sp. ind. Figures 4-2a, b Genus (Parallelodon) ? et sp. ind. Frebold, 1937, p. 56, pl. 2, fig. 4. Material—One incomplete, right external cast. Reg. no. HP 100051. Description.—Posterodorsal marginal part is missing. Preserved part of the specimen is 30 mm long and 18.5 mm high. His twice as long as high judging from the growth line. Surface is covered by numerous, close-set radial striae and Table 1. Measurements of Acanthopecten licharewi (Fredericks). in growth lines which are very weak, but visible under the magnifying glass. The radials reach about forty per centimetre width on the medial part of the shell, one centimetre from the umbo (Figure 4-2b). Discussion.—The present material most probably belongs to the species doubtfully referred to Parallelodon by Frebold (1937) from Festningen. It is similar to G. (C.)? suzuki in shape, but differs from it in more densely spaced and more irregular radial ornament. In its numerous radial striae it is similar to Grammatodon multistriatus (Girty), but it has a different shape with a more convex ventral margin than the latter species. Evidence is not adequate to support a new species for this specimen. Occurrence.—Locality and horizon are identical with those for the preceding species. Order Pterioida Newell, 1965 Superfamily Pectinacea Rafinesque, 1815 Family Aviculopectinidae Meek and Hayden, 1864 Subfamily Aviculopectininae Meek and Hayden, 1864 Genus Acanthopecten Girty, 1903 Acanthopecten licharewi (Fredericks, 1915) Figures 4-3—5 Pterinopecten Licharewi Fredericks, 1915, p. 28, pl. 1, fig. 14. Aviculopecten (Acanthopecten ?) licharewi (Fredericks). Lichar- ew, 1927, p. 91, pl. 6, fig. 24. Acanthopecten licharewi (Fredericks). Muromtseva, 1984, p. 66, pl. 25, fig. 26; pl. 28, figs. 7, 8, 11, 12. Materials.—One nearly complete and one incomplete external cast of left valves, an incomplete external mold of a left ? valve, and an incomplete external mold of a right valve. Reg. nos. HP 100052~55. Description.—All the specimens are incomplete internal molds or somewhat abraded external casts, and the details of the ornament are imperfectly preserved. Shell small, subequivalve, subcircular in shape ; left valve a little inflated ; right valve nearly flat ; anterior auricle of left valve trigonal and sharply defined ; posterior auricle relative- ly large, flat, alate and protruding posterodorsally, but not sharply defined from the disc. Shape variable, probably due to secondary deformation; one left valve of nearly equal height and length, with an apical angle of 100° (Figure 4-3) and another left valve more elongate (L/H ratio of 1.34) with Abbreviations and notation of Tables 1-8. L: length, H: height, U: distance of umbo from the anterior end of the shell, |: hinge length, r: total number of radial ribs, r,, : number of primary and secondary radials, respectively, ro_, : secondary to fourth-order radials between primary radials, r3., : number of number of third- and fourth-order radials between primary and secondary radials, c: number of comarginal lamellae or costae, a: apical angle (in degrees), V: valve (R: right, L: left), *: estimated value, linear dimensions in mm, Hor. : horizon. Reg. no. L H H/L a r c V Hor. HP 100052 23.0 19.5* 0.85 100 13 11 L AP 6 HP 100055 20.5. — — 120 17 94 R AP 6 HP 100054 28.5 22, — — 14, 6. R AP 6 HP 100053 14. 14.8 = = 8, 7 L SA 7 Keiji Nakazawa Permian bivalves from West Spitsbergen 7 a larger apical angle, 120°; radial ribs narrow and widely spaced varying in number from 13 to 17; interspaces between radials slightly concave or nearly flat; lamellose comarginal sculpture widely disposed, becoming wider later in growth stage with distally oriented spines in the middle of the interspaces of the radial ribs (Figure 4-5). Discussion.—This species is similar to the Lower Permian Acanthopecten licharewi (Fredericks, 1915) from the Urals, Pechora and Verkhoyansk, and to the Upper Carboniferous Acanthopecten carbonarius (Stevens) reported from the United States (e.g., Newell, 1938), China (Chao, 1927), and the Donetz Basin (Jakowlew, 1903) in its small size and relatively small number of radial ribs. According to Muromtseva (1984), A. licharewi is distinguished from A. carbonarius in having less numerous radial ribs and completely flat interspaces between the radials. In these respects, the present material is identical with A. licharewi. Occurrence.—Rare in calcareous shale or muddy siliceous limestone of Unit5 (lower part of Hovtinden Member) at Ahlstrandodden (AP 6), and in black shale of Unit 7 (upper part of Svenskeegga Member) at Skansbukta (SA 7). According to Thore S.Winsnes (personal communication, 1995) it also occurs in Permian strata in the valley north of Stensiöfjellet, inner Sassendalen. Subfamily Etheripectininae Waterhouse, 1982 Genus Etheripecten Waterhouse, 1963 Discussion. —This genus was introduced by Waterhouse (1963) based on Etheripecten striatura Waterhouse from the Upper Permian of New Zealand. The ornament of the left valve resembles that of “Aviculopecten” with radial ribs increasing in number by insertion and differentiated into more than two orders. The radial ribs of the right valve of this species also increase in number by insertion, but are usually weaker and less differentiated than those of the left valve. In “Aviculopecten”, the number of radial ribs of the right valve increases by bifurcation or ramification. In this respect, Etheripecten is similar to Limipecten, but according to Waterhouse (1969) the concentric lamellae between radial ribs of Etheripecten point dorsally, while those of Limipecten point ventrally as in the case of Aviculopecten planoradiatus M'Coy, the type species. Recently, Newell and Boyd (1995) reexamined the Late Paleozoic pectinoids. They defined Aviculopecten and Aviculopectinidae as bivalves with equiconvex shells, provided with simple plicae in both valves. On the other hand, the family Etheripectinidae is character- ized by inequiconvex and paradiscordant shells, with multi- costate ornament. Newell and Boyd stressed the variability of multiplicated ribbing and concentric sculpture in this family, treating the genera Aviculopecten and Deltopecten of authors, Etheripecten Waterhouse, Paradoxipecten Zhang, Corrugopecten Waterhouse, Fletcheripecten Waterhouse and Squamuliferipecten Waterhouse as synonyms of Heter- opecten Kegel and Costa. In this case, Heteropecten contains a vast number of species with various kinds of ornamentation. In this paper, Etheripecten is treated as a distinct genus from Heteropecten, the type species of which, Aviculopecten catharinae Reed, has broad and bifurcated radial ribs in the right valve. Fletcheripecten and Paradox- ipecten are here considered to be synonyms of Etheripecten. Etheripecten keyserlingiformis (Licharew, 1927) Figures 4-6, 7a, b Pecten (Aequipecten) ? keyserlingiformis Licharew, 1927, p. 33, pl. 3, figs. 1-3; Frebold, 1937, p. 52, pl. 7, fig. 7. Aviculopecten keyserlingiformis (Licharew). Muromtseva, 1984, p. 60, pl. 28, fig. 10. Materials.—One nearly complete, left semiexternal cast (HP 100056) and one incomplete, left internal mold (HP 100057). Description.—Shell medium in size, pectiniform, a little inflated, prosocline, extended posteroventrally ; disc fan-like in shape with slightly arcuate anterodorsal, nearly straight posterodorsal, and rounded ventral margins ; anterior auricle trigonal with slightly convex anterior margin; posterior auri- cle a little larger than anterior one, sinuated posteriorly ; hinge margin straight, shorter than shelllength ; ligament area narrow, nearly smooth, provided with a trigonal alivin- cular ligament pit beneath the umbo (Figure 4-7b) ; umbo not prominent, slightly salient above the hinge margin, situ- ated at about anterior two-fifths of shell length; surface ornamented with nine or ten slender primary radial ribs alternating with secondaries, some of which become as strong as the primaries; two or three radial riblets of third and fourth order inserted in each interspace ; strong con- centric folds developed over the whole surface of the disc, more widely spaced in later growth stage ; three radial ribs observable on anterior auricle, and obsolete ones on poste- rior auricle. Discussion.—These specimens are identical with Pecten (Aequipecten) keyserlingiformis reported by Licharew (1927) and Frebold (1937), in its characteristic ornamentation. Probably due to secondary deformation, one specimen (Fig- Figure 4. 1a,b. Grammatodon (Cosmetodon) ? suzukii sp. nov., 1a: a pair of external molds of left and right valves, holotype (HP 100050), 1b: enlarged figure showing details of sculpture, x 2.5. 2a,b. Grammatodon (Cosmetodon) ? sp. 2a: right external cast (HP 100051), 2b: enlarged figure showing details of sculpture, x4. 3-5. Acanthopecten licharewi (Fredericks), 3,4: left semiexternal casts (HP 100052 and 53), «2 and 1.5, 5: right external mold (HP 100054), «1.5. 6, 7a, b. Etheripecten keyserlingiformis (Licharew), 6: left semiexternal cast (HP 100056), 7a: left semiexternal cast (HP 100057), 7b: enlarged figure showing alivincular ligament pit (arrow), «2.5. 8,9. Etheripecten wilczeki (Toula), 8: gypsum cast of left external mold (HP 100058), «1.5, 9: left external mold (HP 100059), x 2. (Chen et al.), gypsum cast of left external mold (HP 100060). cast of left external mold (HP 100062), 12: left semiexternal cast (HP 100071). indicated. 10. Etheripecten sp. aff. E. sichuanensis 11,12. Etheripecten sp. cf. E. mutabilis (Licharew), 11: gypsum All are in natural size unless otherwise 8 Keiji Nakazawa Table 2. Measurements of Etheripecten keyserlingiformis (Licharew). Reg. no. E H H/L Nee Ia44 a G Hor. HP 100056 45.5 40.0 0.89 18 3 115 15 F11 HP 100057 = 17.6 — 15, 1~2 90 11 F11 ure 4-6) is extended posteroventrally and has a more elon- gated shape than the previously described species, but another (Figure 4-7a) has a shape and ornamentation similar to the type specimen. Although the right valve of this species has not been reported, the shape and ornamentation of its left valve are very similar to those of Etheripecten Striatura Waterhouse, the type species of the genus, so the species is here included in Etheripecten. Occurrence.—Rare in black shale of the uppermost fossil horizon of the Hovtinden Member at Festningen (F11). Etheripecten wilczeki (Toula, 1875) Figures 4-8, 9 Pecten (Aviculopecten) Wilczeki Toula, 1875a, p. 152, pl. 1, fig. 12. Pecten wilczeki Toula. Frebold, 1937, p. 54. Materials. —One nearly complete, left external mold and several fragmental molds of left valves. Reg. nos. HP 100058, 59. Description.—Shell relatively small, pectiniform, a little inflated ; fan-like in shape, with nearly straight anterodorsal, slightly dorsally arcuate posterodorsal, and rounded ventral margins ; prosocline, extended posteroventrally; umbo not prominent, slightly salient above the hinge margin, lying at about anterior two-fifths of shell length; apical angle 95- 110° ; anterior auricle small, trigonal ; posterior auricle a little larger than the posterior one, alate with arcuate posterior margin ; both auricles sharply distinct from disc ; surface of the shell ornamented with nine primary radial ribs; wide, nearly flat interspaces are sculptured by 8-12 weak, radial threads, some a little stronger than the rest referred to as secondary ribs, but not alternating with the primaries ; um- bonal part of the shell, to 16 mm, ornamented with concentric wrinkles, which later fade away; two or three radial striae discernible on both auricles ; ligament unknown. Comparison.—The type specimen described by Toula has seven strong, slender radial ribs, and smooth interspaces without finer radial ribs. Pecten (Aequipecten) ? wilczekifor- mis Licharew (1927, p. 35, pl. 3, figs. 4, 6, 7) is distinguished from E. wilczeki in its development of interstitial radial riblets. According to Frebold (1937) the type specimen of E. wilczeki is not well preserved. He recognized the presence of finer radial ribs in the marginal area of his specimen, where the shell is preserved, and regarded the two species as being conspecific. However, the finer interstitial radial ribs of the specimen described here are very weak, numer- ous and subequal in strength, whereas those of P.(A.) ? wilczekiformis are differentiated into second, third or even fourth orders. Both species are considered to belong to Etheripecten. E. wilczekiformis is more closely allied to E. keyserlingiformis than to E. wilczeki. E. wilczeki is most similar to Euchondria cancellata Gu and Liu (1976, p. 171, pl. 12, figs. 17, 18), from the Lower Permian Kufeng Series of South China, in shape and ornament. It differs only a little from the latter species in its lesser development of concentric folds and greater height relative to length. The genus Euchondria is characterized by a costate left valve, a nearly smooth right valve, and a series of ligament pits perpendicular to the hinge margin, in addition to a large, central ligament pit. In E. cancellata only left valves are known and the hinge character is unknown. Therefore, its generic position is uncertain. Occurrence.—Rare in calcareous shale of the uppermost horizon of the Svenskeegga Member at Festningen (F5); rare in muddy limestone of the upper part of the Hovtinden Member at Ahlstrandodden (AP 7, 8) and Reinodden (RP 9). Etheripecten sp. aff. E. sichuanensis Chen, Zhang and Xu, 1974 Figures 4-10 Resembles.— Etheripecten sichuanensis Chen, Zhang and Xu, 1974, p. 302, pl. 158, figs. 14,17 ; Fang, 1987, p. 373, pl. 2, figs. 1-6. ? Etheripecten sichuanensis Liu, 1976, p.179, pl. 13, figs. 10-13 ; Gan and Yin, 1978, p. 336, pl. 14, figs. 17, 20. Etheripecten hunanensis Zhang, 1981, p. 261, pl. 2, figs. 6-8. Material.—One incomplete left external mold obtained by dissolving away shell material. Reg. no. HP 100060. Description.—Shell relatively large, a little inflated, longer than high, estimated to be 65mm long and 58mm high; disc fan-like in shape with straight antero- and posterodor- sal margins and a broadly rounded ventral margin; hinge margin straight, a little shorter than shell length; anterior auricle small, subtrigonal, a little inlated, clearly separated from the disc by a sulcus; posterior auricle large, flat, sinuated posteriorly, protruding posterodorsally ; umbo sub- dued, slightly salient above hinge margin; apical angle 110° ; surface ornamented with radial ribs of three orders; pri- maries seven in number, strong and round-topped, alternat- ing with weaker secondaries ; five to six, thread-like rdial riblets of third order inserted in each interspace ; auricles with radial and concentric sculpture making a lattice orna- ment ; hinge not preserved. Discussion.—The external shape and the ornamentation indicate a close relationship of this species with Etheripecten sichuanensis Chen, Zhang and Xu (1974) and E. hunanensis Zhang (1981), both from the Upper Permian Luntang Series in South China. The former species was later illustrated as ? E. sichuanensis sp. nov. by Liu (1976) based on the same specimens. Zhang distinguished E. hunanensis from E. si- chuanensis by the presence of striations and spinose pro- jections on the primary ribs. According to Fang (1987), however, these differences represent infraspecific variation. Permian bivalves from West Spitsbergen 9 The specimen described here differs from sichuanensis in its more elongate shape with larger apical angle and larger size. Occurrence.—Arenaceous limestone of the upper part of the Hovtinden Member at Festningen (F8). Etheripecten sp. cf. E. mutabilis (Licharew, 1927) Figures 4-11,12; Figures 5-1—4 Pecten (Aequipecten) Kokscharofi Toula (non Verneuil), 1873, p. 20, pl. 5, fig. 6. Aviculopecten cf. hiemalis Salter. figs. 18-21 ; pl. 6, fig. 1. ? Aviculopecten (Deltopecten) cf. mutabilis Licharew and A. cf. hiemalis Salter. Frebold, 1937, p. 51, pl. 1, figs. 2, 3. Compared with.— Pecten (Aequipecten) Bouei Toula, 1873, p. 19, pl. 5, fig. 8. Aviculopecten mutabilis Licharew, 1927, p. 72, pl. 5, figs. 7-10, 12, 14-17. Aviculopecten (Deltopecten) ? mutabilis Licharew. Lyutkevich and Lobanova, 1960, p. 102, pl. 15, figs. 1-6. Licharew, 1927, p. 76, pl.5, Material.—Eight incomplete left valves, one complete and two incomplete right valves. Reg. nos. HP 100061~68, 100070, 71. Description.—Shell moderate in size, inequivalve, in- equilateral, prosocline, nearly as long as high, apical angle 90-100°. Left valve moderately inflated ; umbo not promi- nent, a little salient above the hinge margin ; beak situated at about anterior one-third of shell length ; disc fan-like in shape with slightly Concave anterodorsal, nearly straight posterodorsal, and well rounded ventral margins ; anterior auricle subtrigonal, with a rounded anterior margin, demar- cated from the disc by a sulcus ; posterior auricle only partly preserved ; surface covered with many radial ribs differ- entiated into three or four orders; primary ribs 7 to 9 in number, strong, round-topped, a little projected at ventral margin ; second- and third- order radials alternating regular- ly with lower-order radials ; some tertiary radials as strong as secondaries ; fourth-order radials very weak, sporadically inserted near the margin; growth lines close-set, curving ventrally on radial ribs and dorsally on interspaces, showing scaly or spinose projections on the primary ribs (Figures 5-1b, 2). Right valve nearly flat; anterior auricle deeply incised below ; posterior auricle subtrigonal, nearly equal in length to the anterior auricle, a little sinuated posteriorly ; numerous radial ribs increasing in number by insertion; first- and second-order radials becoming subequal in strength; a Table 3. Measurements of Etheripecten sp. cf. E. mutabilis (Licharew). radial ribs, #: total number of radial ribs. small number of third-order radials, very weak and thread- like ; total number of radials, 34 ; close-set, weak concen- tric sculpture, making a lattice ornament with the radials ; alivincular ligament pit partly seen in one left internal mold. Remarks and comparison.—In this material, the number of radial ribs increases by insertion in both the left and right valves. The comarginal sculpture curves ventrally on the radial ribs and dorsally on the interspaces. Therefore, these specimens are referred to Etheripecten Waterhosue (1969). In their well differentiated radial ornament and robust primary radial ribs, these shells are identical with Pecten (Ae- quipecten) kokscharofi as described by Toula (1873), Aviculopecten cf. hiemalis Licharew (1927), and probably Aviculopecten (Deltopecten) cf. mutabilis and A. (D.) cf. hiemalis Frebold (1937). They are very similar to Aviculopecten mutabilis Licharew (1927). According to Licharew (1927) the latter species is distinguished from Aviculopecten cf. hiemalis by its more pointed posterior auricle, the sharper restriction of auricles from the disc, the weaker bend of antero- and posterodorsal margins of the disc, and less regularity in the appearence of ribs. These differences, though, are not distinctive, as noted by Licharew himself. A. cf. hiemalis of Licharew has generally more robust primary radials than A. mutabilis. It is clearly distin- guished from the original A. hiemalis reported from the Himalayas (cf. Diener, 1897, p. 9, pl. 5, figs. 10a, b, 11) in taller shape and smaller posterior auricle and is more closely related to A. mutabilis. Lyutkevich and Lobanova (1960) illustrated the right valve of A. mutabilis (pl. 15, figs. 2, 5), which shows inserted radial ribs. Therefore, A. mutabilis is considered to belong to the genus Etheripecten. The right valve of Etheripecten mutabilis has less uniform radial orna- ment than the present species. Occurrence.—Common in the Hovtinden Member at Fest- ningen, Reinodden, and Ahlstrandodden; rare in Svens- keegga Member at Reinodden. Etheripecten ? sp. cf. E. alatus (Lyutkevich and Lobanova, 1960) Figures 5-5 Compared with.— Pseudomonotis alata Lyutkevich and Lobanova, 1960, p. 116, pl. 17, fig. 9. Description.—Only one incomplete, semiexternal cast of a “x : Total number of primary and secondary Reg. no. ik H H/L U U/L ia 1253 a V Hor. HP 100060 60. 58. = = = le 4~6 100 L F9 HP 100062 21.5 22.8 1.06 = = 7 3 85 L RP 3 HP 100063 22.3 21.5 0.96 8.0 0.36 26% 90 R F 11 HP 100064 30. ei). _ _ = 6, 3~4 — E F 9 HP 100065 83.5 35.0 1.04 12.5 0.37 9 3~5 90 E F 11 HP 100066 21.0 — = = = 244 85 R F 11 HP 100067 25.0 25.0 1.00 165 0.30 8 3~4 90 (Es F 11 HP 100071 25.3 257 1.02 10.5 0.42 th 3 90 L F 7p 10 Keiji Nakazawa Permian bivalves from West Spitsbergen 11 left? valve is available (Reg. no. HP 100069). More than posterior one-third of the shell is not preserved. Shell 38 mm high and more than 30 mm long, nearly flat; disc in- ferred to be fan-like in shape ; anterodorsal margin straight ; anterior auricle trigonal, flat, clearly marked off from the disc ; surface ornamented with six strong, round-topped primary radial ribs ; broad, flat or slightly concave interspaces with weak secondary and tertiary radials five to eight in number ; close-set weak concentric striae partly preserved. Discussion.—The present material is quite similar in shape and sculpture to Pseudomonotis alata, described on the basis of a right valve by Lyutkevich and Lobanova (1960) from the Lower Permian at Pai Khoi of the northern coast of Siberia. It differs slightly from that species in taller outline. The well differentiated, straight radial ornament of these Siberian and Spitsbergen species suggests that they belong to Etheri- pecten rather than to Pseudomonotis. Occurrence.—Dark grey calcareous shale of Unit G of the Hovtinden Member at Reinodden (RP 9). Family Streblochondriidae Newell, 1938 Genus Streblochondria Newell, 1938 Streblochondria winsnesi sp. nov. Figures 6-2a, b—4 Pecten (Pseudamusium) cf. ufaensis Tschernyschew. Frebold, 1937, p. 53, pl.1, fig. 3-5. Material —One complete right valve (external and internal molds, holotype, Reg. no. HP 100094a, b) and a nearly complete right valve (internal and external molds, Reg. no. HP100095a, b). Holotype specimen occurs in black shale of Unit 11 of the Hovtinden Member at Festningen. Etymology.—Dedicated to Thore S. Winsnes for his contri- bution to the geological understanding of West Spitsbergen. Diagnosis.—Permian Streblochondria characterized by a broad shape and very fine cancellate ornament composed of numerous radial and concentric striae. Description.—Shell medium in size, a little inflated, and subcircular in shape, with well rounded ventral, slightly convex posterodorsal, and slightly concave anterodorsal margins; as long as high; opisthocline ; umbo subdued, not salient above the hinge margin; apical angle varying from 90° to 110° ; posterior auricle very small, obtuse-triangu- lar, truncated posteriorly; anterior auricle relatively large, rounded trigonal, and marked below by deep slit-like byssal notch ; surface covered with numerous, uniform radial striae increasing in number by insertion, 70 per cm in the medial area 1cm away from the umbo; dense concentric fila Table 4. Measurements of Streblochondria winsnesi sp. nov. Reg. no. EE H H/L | a Hor. HP 100094 33.5 ca33 099 95 90-110 F11 HP 100095 20.0 20.0 1.00 = 90-110 APQ making a cancellate ornament with the radials, slightly raised scales on the radials ; anterior auricle ornamented with five distinct radial ribs and growth lines; hinge characters un- known. Discussion.—Frebold (1937) illustrated three right valves identified as Pecten (Pseudamusium) cf. ufaensis Tscherny- schew from the upper part of the Kapp Starostin Formation at Festningen. One of them shows a distinct sculpture, very similar to that described here, so it is considered to be conspecific with this species. It is similar to Streblochondria sculptilis (Muller), the type of the genus, from the Carbonifer- ous of the United States (cf. Newell, 1938, p. 38, pl. 16, figs. 5a-c, 7, 9a, b). However, the present new species has a larger apical angle, a lower outline, and finer ornament than that species. It is more closely allied to S. ufaensis (Tscher- nyschew) (Licharew, 1927, p. 30, pl. 2, figs. 7,8; Lyutkevich and Lobanova, 1960, p. 131, pl. 21, fig. 1), but differs from that species in the finer radial sculpture as noticed by Frebold and, furthermore, in its longer outline. Occurrence.—Rare in siliceous limestone of the upper part of the Hovtinden Member at Ahlstrandodden (AP 9), and the uppermost horizon of the Hovtinden Member at Festningen (F11). Genus Streblopteria M'Coy, 1851 Streblopteria sp. cf. S. eichwaldi (Stuckenberg, 1898) Figures 6-6, 7a, b, c Pecten (Aviculopecten) cf. ellipticus Toula, 1873, p. 20, pl. 5, fig. 1. Pecten (Pseudamusium) sp. ind. ex aff. sericeus Frebold, 1937, p. 54. Compared with.— Pecten Eichwaldianus Stuckenberg, 1898, p. 208, pl. 1, figs. 25a, b. Materials.—A pair of valves, two internal molds, and two incomplete external molds. Reg. nos. HP 100087~90. Description.—Shell small, nearly equivalve, subcircular in shape, opisthocline, a little extended anteriorly ; left valve gently inflated; right valve slightly less convex than left; anterodorsal margin of the disc a little concave, ventral and posterior margins well rounded ; umbo lying a little posterior to the middle of the shell, not salient above the hinge Figure 5. 1-4. Etheripecten sp. cf. E. mutabilis (Licharew), 1a: gypsum cast of left external mold (HP 100061), 1b: enlarged figure showing details of sculpture, «3, 2: gypsum cast of left external mold (HP 100064), 3: silicon rubber cast of right external mold (HP 100066), 4: gypsum cast of right external mold (HP 100063). (Lyutkevich and Lobanova), left? semiexternal cast (HP 100069). 5. Etheripecten ? sp. cf. E. alatus 6-10. Vorkutopecten svalbardensis sp. nov., 6: gypsum cast of right external mold, holotype (HP 100072), 7 : semiinternal mold of left valve, paratype (HP 100076), 8: gypsum cast of right external mold (HP 100075) «1.2,9: gypsum cast of right external mold (HP 100077), 10: gypsum cast of right external mold (HP 100078), x 1.4. cast of external mold of right valve (HP 100086). 11,12. Deltopecten sp., 11: semiexternal cast of left valve (HP 100085), 1.1. All are natural size unless otherwise indicated. 12: silicon rubber Keiji Nakazawa 12 Permian bivalves from West Spitsbergen 13 margin ; apical angle 90° in umbonal portion and 110-120" in later growth stages ; posterior auricle small, obtuse-triangu- lar; anterior auricle larger, obtuse-triangular in left valve, and deeply incised below in the right valve ; surface almost smooth, weak concentric sculpture discernible in the internal mold and partly preserved external cast ; no radial ornament observed. Discussion and comparison.—The genus Streblopteria was established by McCoy (1851). The Carboniferous Meleagrina laevigata McCoy from Ireland was designated as type species by Meek and Worthen (1866). The genus is char- acterized by smooth shells of acline to opisthocline pectinoid form, and is distinguished from Streblochondria Newell (1938) which has cancellate sculptures. The posterior auricle of the type species is much larger than the anterior auricle, poorly distinguished from the disc. However, the forms with a small, obtuse-triangular, more or less clearly defined posterior auricle are also included in Streblopteria or referred to Pseudamusium Verrill by many authors. According to Cox et al. (1969) Pseudamusium is a junior synonym of the Cenozoic genus, Palliolum Monterosato. Several small Pseudamusium species, such as P. eichwaldi (Stuckenberg), P. pusillus (Schlotheim), and P. ellipticum (Phil- lips), have very weak radial ribs or cancellate ornament on a limited part of the shell. They were doubtfully assigned to Streblochondria by Newell (1938). However, they have a longer shape than Streblochondria and are more similar to smooth forms of Streblopteria or “Pseudamusium”. This hardly warrants recognition as a different genus. In this paper, all these species are treated as Streblopteria, although they differ somewhat from the type species. The species described here is most similar to S. eichwaldi (Stuckenberg, 1898) in shape, but the surface ornament is insufficiently known for specific identification. Pecten cf. ellipticus reported by Toula (1873) from the south point of Spitsbergen was referred to Pecten (Pseudamusium) aff. sericeus Verneuil by Frebold (1937). However, P. sericeus has a more opisthocline shell that is extended more anterior- ly. It is probably identical with the present species. Occurrence.—Siliceous limestone of the lower part of the Hovtinden Member at Ahlstrandodden (AP 6). Streblopteria ? sp. ind. Figures 6-8 Discussion.—One incomplete right internal mold (Reg. no. HP 100092), estimated at 24 mm long and a little more than 24 mm high, is at hand. The shell is subcircular in outline and provided with a concave anterodorsal margin. The surface is covered by a weak concentric sculpture. The auricular part of the shell is not preserved. It probably belongs to Streblopteria, but is too imperfectly preserved to be certain. Occurrence.—Siliceous shale of the lower part of the Hovtinden Member at Ahlstrandodden (AP 6). Family Deltopectinidae Dickins, 1957 Genus Vorkutopecten Guskov, 1984 Vorkutopecten svalbardensis sp. nov. Figures 5-6—10 Material.—Eight right external and internal molds and three left external and internal molds. Reg. nos. HP 10007283 (holotype HP 100072). Holotype from Unit 9 of the Hovtin- den Member at Festningen. Etymology.—Derived from Svalbard Islands, where the species occurs. Diagnosis.—Shell is higher than long ; ornamentation of both left and right valves consists of numerous radial ribs differentiated into three orders, increasing in number by insertion. Concentric costae arch ventrally in the inter- spaces of radial ribs. Description.—Shell inequivalve, inequilateral, suborbicular in shape, a little higher than long ; right valve moderately to weakly inflated ; left valve more inflated than right; umbo situated a little anterior to the middle of shell, nearly acline and slightly salient above the hinge margin in the left valve, but not in the right valve; apical angle about 90°; anterior and posterior auricles nearly equal in length; posterior one trigonal and sinuated posteriorly ; right anterior auricle deep- ly incised below; surface of disc covered with numerous, slender radial ribs narrower than interstices, increasing in Table 5. Measurements of Streblopteria sp. cf. S. eichwaldi (Stuckenberg). Reg. no. [E H H/L | YL U U/L a V Hor. HP 100087a 8.0 TS 0.94 4.0 0.50 4.0 0.50 ~110 L AP 6 HP 100087b 8.0 78 0.98 ST 0.46 4.5 0.56 90-120 R AP 6 HP 100088 12.7 11.6 0.91 5 0.45 7.2 0.56 90-120 R AP 6 HP 100089 13.0* 12.5 0.96 = — 7.5 0.57 ~120 R AP 6 Figure 6. 1. Vorkutopecten sp. aff. V. svalbardensis sp. nov., gypsum cast of right external mold (HP100084). 2-4. Streblochondria winsnesi sp. nov., 2a: right external mold, holotype (HP 100094), «1.4, 2b: gypsum cast, 3: right internal mold of the same, 4: right external mold (HP 100095). 5. Cassianoides sexcostatus (Stuckenberg), left external mold (HP 100093), X 2.4. 6, 7a-c. Streblopteria sp. cf. S. eichwaldi (Stuckenberg), 6 : right internal mold (HP 100088), «1.5, 7a: a pair of internal molds of left (L) and right (R) valves (HP 100087), «2, 7b-c: enlarged figures of right (b) and left (c) valves, <3. 8. Streblopteria ? sp., right external cast (HP 100092). 9,10. Palaeolima nakamurai sp. nov., 9: right external cast, paratype (HP 100097), “1.5, 10: right external cast (R), holotype (HP 100096) and a part of left valve (L), x1.2. All are natural size unless otherwise indicated. 14 Keiji Nakazawa number by insertion; primary radial ribs varying in number from 12 to 17, with two or three radials of second and third orders in each interspace between the primaries ; total number of radials 35 to 50 or more; secondary radials of right valve become as strong as primaries ; lamellose con- centric sculpture developed on the whole surface, curving dorsally on radial ribs and ventrally in interstices; both auricles sculptured by radial ribs and concentric costae; a small, trigonal ligament pit partly preserved in one left internal mold. Remarks and comparison.—The radial ribs of both left and right valves increase in number by insertion, as in Etheri- pecten, Limipecten, and Vorkutopecten. The concentric sculpture swings ventrally between radial ribs as in Limipecten, not Etheripecten. The shell length of Limipecten is usually equal to or larger than the height, and the radial ribs of the right valve are finer and more numerous than those of the left valve. Furthermore, the right valve is nearly flat. The present species has a greater height than length. The ornamentaion is similar in both valves, although secondary ribs of the right valve grow as strong as the primaries. The right valve is more or less inflated. In these respects, it can be identified with Vorkutopecten established by Guskov (in Muromtseva, 1984), based on Aviculopecten giganteus talis Lyutkevich and Lobanova (1960, p. 108, pl. 16, fig. 10; pl.17, fig. 1). Guskov included two species in the genus in addition to the type species, namely, Aviculopecten subclathratus (Keyserling) and A. netschajewi Licharew. However, the type specimen of the latter species has bran- ching radial ribs in the right valve and is excluded from Vorkutopecten. On the other hand, materials described as Vorkutopecten netschajewi by Guskov (Muromutseva, 1984, pl. 29, fig. 8) have inserted radial ribs and cannot be identified with this species, which is more similar to A. subclathratus. The Spitsbergen species is similar to A. subclathratus and A. netschajewi of Guskov, but differs in its more numerous primary radial ribs and larger posterior auricle. Vor- kutopecten, characterized by broad, alivincular ligament pit and a grooved ligament area, is included in Family Deltopectinidae. The present species has a relatively small ligament pit. Occurrence.—Common in siliceous limestones of the Hovtinden Member at Festningen (F 7p, F 8 and 9), rare in limestone of the Voringen Member (AP 1), common in siliceous limestone of the Svenskeegga (AP 2) and the Hovtinden Member (AP 6, 7) at Ahlstrandodden, rare in cal- careous sandstone of the Hovtinden Member at Reinodden (RP 7). Vorkutopecten sp. aff. V. svalbardensis sp. nov. Figures 6-1 Discussion.—The species is represented by a single, large external mold of a right vaive (Reg. no. HP 100084). It is 86 mm long and 91mm high and has an apical angle of 100°. The shell is gently convex and sculptured with as many as 60 radial ribs. The radials are differentiated into three orders, but due to poor preservation distinction between primary and secondary ribs is difficult. This species is very similar to the preceding new species in shape and ornamen- tation, but its size is much larger and its apical angle is a little greater. Occurrence.—Arenaceous limestone of Unit1 (Vgringen Member) at Ahlstrandodden (AP 1). Genus Deltopecten Etheridge, Jr., 1892 Deltopecten sp. ind. Figures 5-11, 12 Material. —One incomplete left semiexternal cast, and one incomplete right valve represented by external and internal molds. Reg. nos. HP 100085, 86. Description.—Shell moderate in size, subcircular in shape, nearly equiconvex and subequilateral ; umbo not prominent, located subcentrally ; apical angle 100-110" ; anterior auricle triangular, with slightly concave anterior margin in the left valve and byssate in the right valve ; left posterior auricle not preserved ; right posterior one partly preserved, obtuse-tri- angular and probably smaller than the anterior one ; surface of the left valve sculptured by relatively slender, rounded primary ribs, 18 in number, separated by wide interspaces and alternating with very weak, secondary radials; right valve ornamented with flat-topped primary radial ribs ; inter- vening flat interspaces of a width nearly equal to that of the radial ribs, with weak secondary radials inserted in the medial part of the shell; surface of both valves covered with close- set concentric fila swinging slightly ventrally, in the inter- spaces ; ligament not preserved. Discussion.—Although the ligament cannot be observed, the present species can be referred to Deltopecten judging from the nearly equiconvex shell and relatively simple, flat- topped radial ribs. This species is somewhat similar to Table 6. Measurements of Vorkutopecten svalbardensis sp. nov. Reg. no. ie H H/L | U/L a r r Vv Hor. HP 100072 SILOF 30.5* 0.98 19. 0.48 88 16 54 R F9 HP 100074 29.0 31.5 1.09 20.0 0.38 90 11? 47 R F 7p HP 100075 35.0 38.0 1.09 35.0 0.46 88 17 46. R F9 HP 100076 24.0* 27.0 113 — 0.46 85 14 30. L AP 1 HP 100077 20.0 22.0 1.10 — 0.50 90 12 42 R F 7p HP 100078 27.0* 28.7 1.06 22.0 0.50 90 12 40 L AP 1 HP 100080 34.3 35.8 1.04 26.0 0.43 90 12 37 R AP 2 HP 100081 26.0* 30.3 dar 13.0 0.49 90 ? 35 R AP 7 Permian bivalves from West Spitsbergen 15 Table 7. Measurements of Deltopecten sp. ind. Reg. no. L H H/L U/L a ri V Hor. HP 100085 35:5 33:5 0.94 16.7 0.47 105 18 [E RP 7 HP 100086 30+ 35.0 — 1725 0.50 110 15? R AP2 Deltopecten Iyonsensis Dickins (1957, p. 41, pl. 7, figs. 1-5 and 9; pl. 8, figs. 11-13; pl.9, fig. 12 ; pl. 10, figs. 3-4) from West Australia, but differs from that species in its less numerous primary radial ribs and the development of secondary radials in the left valve. Occurrence.—Rare in calcareous sandstone of Unit E of the Hovtinden Member at Reinodden (RP 7) and in siliceous limestone of Unit 3 of the Svenskeegga Member at Ahlstran- dodden (AP 2). Family Cassianoididae Newell and Boyd, 1995 Genus Cassianoides Newell and Boyd, 1995 Discussion.—The present family and genus were estab- lished by Newell and Boyd (1995) on the basis of a single species, Cassianoides kingorum Newell and Boyd of the Middle to Late Permian of West Texas. The genus is characterized by small, strongly inequivalve shells ; the left valve is strongly convex, ornamented with a few widely spaced, strong primary costae and a few comarginal, tubular hyote spines on the radial ribs ; the right valve is flat, sculp- tured by spineless, subdued radial ribs. Cyrtorostra sex- radiata Branson (1930, p. 45, pl. 11, figs. 13-15) from the Upper Permian Park City Formation was later shifted to the genus Cassianella of the Family Cassianellidae by Ciriacks (1963). This species was considered to be a junior synonym of Pseudomonotis sexcostatus Stuckenberg (1898, p. 207, pl. 1, fig. 40) from the Permian of Russia and to belong to Aviculopecten by Muromtseva (1984). The species is very similar to Cassianoides kingorum, not only in shell form but also in the characteristic ornamentation of both the left and right valves. It undoubtedly belongs to Cassianoides. Aviculopecten crassispinosus Chronic, reported by Newell et al. (1953, p. 155, pl. 33, figs. 10-13) from the Lower Permian of Peru, is also referred to as a member of this genus. Cassianella rara described by Waterhouse (1987, p. 145, pl 3, figs. 1, 7,10) from the Middle Permian of East Australia is another example. Waterhouse noticed the close relation of this species to C. sexradiata and C. crassispinosus. His figs. 1 and 7, illustrated as a right valve, are quite similar to the left valve of A. crassispinosus (especially fig. 13a of Newell et al., 1953), and are believed to be a left valve. The genus Crassinoides is now known from the Permian of the United States, Peru, Australia, Russia, and Spitsbergen. Cassianoides sexcostatus (Stuckenberg, 1898) Figure 6-5 Pseudomonotis sexcostatus Stuckenberg, 1898, p. 207, pl. 1, fig. 40. Cyrtorostra sexradiata Branson, 1930, p. 45, pl. 2, figs. 13-15. Cassianella sexradiata (Branson). Ciriacks, 1963, p. 45, pl. 5, figs. 5-7. Aviculopecten sexcostatus (Stuckenberg). 61, pl. 27, fig. 6; pl. 33, figs. 10-13. Muromtseva, 1984, p. Material.—Only one external mold of a left valve. HP 100093. Description.—Shell small, 14mm long and 14mm high, strongly inflated ; umbo narrow, orthogyrate, salient above the hinge margin and curving down over the hinge ; anterior auricle rounded-trigonal, a little inflated and marked off from the disc by a deep and wide sulcus ; posterior auricle imper- fectly preserved, relatively small, obtuse-triangular, with its posterior margin weakly sinuated and set off from the disc by a strong, posterior, radial marginal rib ; surface ornamented with nine slender but sharply raised radial ribs, projecting ventrally at ventral margin; interspaces between radials wide, slightly concave; distinct, regular concentric fila, closely spaced, curving dorsally in the interspaces, and with comarginal spinose projections on the radials ; hinge margin straight, shorter than shell length; hinge not preserved. Remarks.—The present specimen differs from the type in its more numerous radial ribs, but this is considered to be due to infraspecific variation. Crassianoides sexcostatus can be distinguished from C. crassispinosus (Chronic) by its weaker radial ribs and less spinose concentric sculpture, and from C. rara (Waterhouse) by the absence of secondary radial riblets. Occurrence.—Black siliceous shale of the uppermost fossil horizon of the Hovtinden Member at Festningen (F1). Reg. no. Superfamily Limacea Rafinesque, 1815 Family Limidae Rafinesque, 1815 Genus Palaeolima Hind, 1903 Palaeolima nakamurai sp. nov. Figures 6-9, 10 Materials.—External casts and molds of a complete right valve and an incomplete left valve, and a nearly complete external cast of a right valve. Reg. nos. HP 100096 (holotype) and 100097. Holotype specimen occurs in shale of Unit 7 of the Hovtinden Member at Festningen. Diagnosis.—Broadly rounded Palaeolima ornamented with wide, rounded, branching radial ribs intercalated with narrow furrows. Etymology.—Dedicated to Dr. K. Nakamura, who surveyed West Spitsbergen several times as a leader of the Japanese Expedition. Description.—Shell equivalve, inequilateral, a little inflated, broad and oblique-oval in shape, opisthocline, extended anteroventrally ; umbo not prominent, a little salient above the hinge margin; apical angle about 110°; umbonal angle about 80°, no umbonal ridge ; umbo situated near the middle of the straight hinge margin; height slightly less than the length; both auricles obtuse-triangular, anterior one Table 8. Measurements of Palaeolima nakamurai sp. nov. longest axis of the shell) Keiji Nakazawa A: umbonal angle (angle between hinge line and Reg. no. [a H H/L U U/L a A r th V Hor. HP 100096 31.0 29.7 0.96 18.8 1.65 80 110 33 15 R F 7-1 HP 100097 24, 24.5 80 110 30 16 R AP 6 depressed, obscurely defined from the main body ; posterior one marked off anteriorly by a steep umbonal slope ; surface ornamented with 15-16 broadly rounded, primary radial ribs wider than interstitials, increasing in number by bifurcation, reaching 30 or more in total; growth lines weak; anterior auricle nearly smooth; posterior one sculptured by weak radial costae ; hinge not preserved. Comparison.—The species is similar in ornament to Palaeolima simplex Hind (1908, p. 39, pl. 39, figs. 24-27) from the Carboniferous of England, P. petaline Zhang (1981, p. 213, pl. 11, figs. 17) and P. fasciculicostata Liu (1976, p. 236, pl. 17, figs. 22, 24, 25), both from the lower Upper Permian of South China. It is distinguished from them by its larger size and more circular outline. Palaeolima krotowi (Stuckenberg, 1898, p. 336, pl.1, fig. 29) from the Upper Carboniferous of Russia has radial ribs narrower than its interstitial furrows and is easily distinguished from the present species. Specimens referred to P. krotowi by Licharew (1927, p. 37, pl. 3, figs. 8-12, 14) and Muromtseva (1984, p. 79, pl. 33, fig. 11), from the Lower Permian of the Urals and Pechora, have broader radials than interstices, so the specific identification is doubtful. These shells are more similar to the present new species than to P. krotowi, but they differ from it being more anteroventrally extended and more oblique in shape. Occurrence.—Rare in black shale of the lower part of the Hovtinden Member at Festningen (F 7-1) and at Ahlstrandod- den (AP 6). References Branson, C.C., 1930: Paleontology and stratigraphy of the Phosphoria formation. Missouri University Studies, vol. 5, p.1-99. Chao, Y., 1927: Fauna of the Taiyuan Formation of North China-Pelecypoda. Palaeontologia Sinica, ser. B, vol. 9, fasc. 3, p. 1-64. (in Chinese) Chen, C.C., Zhang, ZM, and Xu, J.T., 1974: Permian Bivalvia. /n, Nanjing Institute of Geology and Palaeontology ed., A Handbook of Stratigraphy and Palaeontology in Southwest China, p. 302-303. (in Chinese) Ciriacks, K.W., 1963: Permian and Eotriassic bivalves of the Middle Rockies. Bulletin American Museum of Natural History, vol. 125, 100 p., 16 pls. Cox, L.R., 1969: Palliolum (Palliolum). In, Moor, R.C. ed., Treatise on Invertebrate Paleontology, Part N, vol. 1, Mollusca 6. Bivalvia, N354, The University of Kansas Press and the Geological Society of America. Cutbill, J.L. and Challinor, A., 1965: Revision of the strati- graphical scheme for the Carboniferous and Permian rocks of Spitsbergen and Bjorngya. Geological Maga- zine, vol. 102, p. 418-435. Dickins, J.M., 1957: Lower Permian pelecypods and gas- tropods from the Carnavon Basin, Western Australia. Bureau of Mineral Resources, Geology and Geophysics, Commonwealth of Australia, Bulletin, vol. 41, 55 p., 10 pls. Diener, C., 1897: The Permian fossils of the Productus Shales of Kumaon and Gurhwal. Memoir Geological Survey of India, Ser. XV Himalayan Fossils, vol. 1, pt. 4, 54 p., 5 pls. Fang, Z.Z., 1987: Bivalves from the upper part of the Per- mian in Southern Hunan, China. Collection of Post- graduate Theses, Nanjing Institute of Geology and Palaeontology, Academia Sinica, no. 1, p. 349-411, pls. 1- 8. (in Chinese with English abstract) Flood, B., Naggy, J. and Winsnes, T.S., 1971: Geological Map Svalbard 1: 500,000, sheet 1G, Spitsbergen South- ern Part. Norsk Polarinstitutt Skrifter, Nr. 154A. Forbes, C.L., Harland, W.B. and Hughes, N.F., 1958: Palaeontological evidences for the age of the Carbonif- erous and Permian rocks of Central Vestspitsbergen. Geological Magazine, vol. 95, p. 465-489. Frebold, H., 1937 : Das Festungsprofil auf Spitsbergen. IV Die Brachiopoden- und Lamellibranchiaten und die Strati- graphie des Oberkarbons und Unterperms. Skrifter Svalbard og Ishavet, vol. 69, p. 1-94, pls. 1-11. Fredericks, G., 1915: Fauna verkhnepaleozoyskoy tolstshi okrestnosty g. Krasnoufimska Permskoy gubernii (Upper Paleozoic fauna of the environment of Krasnoufimsk). Mémoires du Comité Géologique, n. ser. vol.109, 117 p., 10 pls. (in Russian with French abstract) Gan, X. and Yin, H., 1978: Lamellibranchiata. In, Working Team on Stratigraphy and Palaeontology of Guizhou Province ed., Palaeontological atlas of Southwest China, volume of Guizhou Province, pt. 2, p. 337-396, pls. 109- 126. (in Chinese) Gee, E.R., Harland, W.B. and McWhale, J.R.H., 1953: Geol- ogy of Central Vestspitsbergen, Part Il. Carboniferous to Lower Permian of Billefjorden. Transactions Royal Society of Edinburgh, vol. 62, p. 299-356. Girty, G.H., 1903 : The Carboniferous formations and faunas of Colorado. United States Geological Survey, Profes- sional Paper, vol. 16, 546 p. Girty, G.H., 1908: The Guadalupian fauna. United States Geological Survey, Professional Paper, vol. 58, 626 p., 31 pls. Gobbet, D.J., 1963 : Carboniferous and Permian brachiopods of Svalbard. Norsk Polarinstitutt Skrifter, vol.127, 201 p., 25 pls. Gu, Z.W. and Liu, L., 1976: Euchondria cancellata, sp. nov. In, Nanjing Institute of Geology and Palaeontology, Academia Sinica ed., Monograph of bivalve fossils of China, p.171. Science Press. (in Chinese) Guskov, B.A., 1984: Genus Vorkutopecten. In, Murom- tseva, V.A. ed., Permian marine deposits and bivalve molluscs of the Soviet Arctic, p.65. Ministry of Geol- Permian bivalves from West Spitsbergen ogy, USSR, Lenigrad, (Nedra). (in Russian) Hind, W., 1901-1905 : Monograph of the British Carbonifer- ous Lamellibranchiata, vol.2, 222p., 25 pls. Palaeontological Society of London. Jakowlew, N., 1903: Die Fauna der oberen Abteilung der paleozoischen Ablagerungen im Donetz-Bassin. |. Die Lamellibranchiata. Mémoires du Comité Geologique, n. ser. vol. 4, 44 p., 2 pls. Japanese-Norwegian Research Group, 1992: Investigation on the Upper Carboniferous-Upper Permian succession of West Spitsbergen, 1981-1991, 134 p. Hokkaido Uni- versity. Kortshinskaya, M.V., 1986: Biostratigraphy of Induan Stage of Spitsbergen. In, Krasilstshikov, A.A. and Mirzaev, M. N. eds., Geology of sedimentary cover of Spitsbergen Archipelago, p. 77-93, pls.1-7. Ministry of Geology, USSR, Leningrad. (in Russian) Licharew, B.K., 1927: Upper Carboniferous Pelecypoda of Ural and Timan. Mémoires du Comité Geologique, n. ser., vol.164, 137 p., 4pls. (in Russian with English abstract) Liu, L., 1976: Etheripecten sichuanensis, sp. nov. In, Nan- jing Institue of Geology and Palaeontology, Academia Sinica eds., Monograph of bivalve fossils of China, p. 179. Science Press. (in Chinese) Lyutkevich, E.M. and Lobanova, O.V., 1960: Permian pelecypods from the Soviet sector of the Arctic. Transactions All-Union Petroleum Scientific-Research Geological-Prospecting Institute (VNIGRI), Bulletin, vol. 149, 218 p., 35 pls. (in Russian) McCoy, F., 1851: Aviculopecten. Annals Magazine of Natu- ral History, vol. 2, p. 171. Meek, F.B. and Worthen, A.H., 1866: Description of inverte- brates from the Carboniferous system. Illinois Geologi- cal Survey, vol. 2, Palaeontology, p. 143-411. Muromtseva, A.V. ed., 1984: Permian marine deposits and bivalve molluscs of the Soviet Arctic, 154 p., 53 pls. Ministry of Geology, USSR, Leningrad (Nedra). (in Russian) Nakamura, K., Kimura, G. and Winsnes, T.S., 1987: Bra- chiopod zonation and age of the Permian Kapp Staros- tin Formation (Central Spitsbergen). Polar Research, n. s. vol. 5, p. 207-219. Nakamura, K., Kimura, G., Winsnes, T.S. and Lauritzen, O., 1990 : Permian and Permian-Triassic boundary in Cen- tral Spitsbergen. In, Tatsumi, T. ed., The Japanese Scientific Expedition to Svalbard 1983-1990, p. 137-153. Kyoikusha, Tokyo. Nakamura, K., Tazawa, J. and Kumon, F., 1992: Permian brachiopods of the Kapp Starostin Formation. In, Japanese-Norwegian Research Group, Investigation on the Upper Carboniferous-Upper Permian succession of West Spitsbergen, 1989-1991, p. 77-95, pls. 1-5. Hok- kaido University. Nakazawa, K., Nakamura, K. and Kimura, G., 1987 : Discov- ery of Otoceras boreale from West Spitsbergen. Pro- ceedings of Japan Academy, vol. 63, p. 171-174. Nakazawa, K., Suzuki, H., Kumon, F. and Winsnes, T.S., 1990: Japanese Geological Expedition to Svalbard in the summer of 1986. /n, Tatsumi, T. ed., The Japanese Scientific Expedition to Svalbard 1983-1990, p. 175-214. Kyoikusha, Tokyo. Newell, N.D., 1938: Late Paleozoic pelecypods : Pectinacea. State Geological Survey of Kansas, vol. 10, 123 p., 20 pls. Newell, N.D. and Boyd, D.W., 1995 : Pectinoid bivalves of the Permian-Triassic crisis. Bulletin of the American Museum of Natural History, no. 227, 95 p. Newell, N.D., Chronic, J. and Roberts, T.G., 1953: Upper Paleozoic of Peru. Geological Society of America, Memoirs, vol. 58, 261 p., 34 pls. Sakagami, S., 1992: Notes on the Permian bryozoans from Kapp Starostin Formation at Festningen route, Spitsber- gen. In, Japanese-Norwegian Research Group, Inves- tigation on the Upper Carboniferous-Upper Permian succession of West Spitsbergen, p. 40-57. Hokkaido University. Stuckenberg, A., 1898: Allgemeine geologische Karte von Russland. Blatt 127. Mémoires du Comité Geologi- que, vol. 16, 361 p., 5 pls. Toula, F., 1873: Kohlenkalk-Fossilien von der Sudspitze von Spitzbergen. Sitzungberichte der keyserlichen Akademie der Wissenschaften in Wien, Mathematisch- naturwissenschaftliche KI., vol. 68, pt. 1, p. 267-291. Toula, F., 1875a: Kohlenkalk- und Zechstein-Fossilien aus dem Hornsund am der Süd-Westküste von Spitzbergen. Sitzungbericht der keyserlichen Akademie, Wien, Mathematisch-naturwissenschaftlich KI., vol. 70, pt.1, p. 133-157. Toula, F., 1875b: Permo-Carbon-Fossilien von der West- küste von Spitzbergen. Neues Jahrbuch für Miner- alogie, Geologie und Paläontologie, 1875, p. 225-264, pls. 5-10. Waterhouse, J.B., 1963: Etheripecten, a new Avicul- opectinid genus from the Permian. New Zealand Jour- nal of Geology and Geophysics, vol. 6, p. 193-196. Waterhouse, J.B., 1969: Growth lamellae on the type species of the Upper Paleozoic bivalve Aviculopecten McCoy. Journal of Palaeontology, vol. 43, p. 1179-1183. Waterhouse, J.B., 1982: Permian Pectinacea and Limacea (Bivalvia) from New Zealand. New Zealand Geological Survey, Palaeontological Bulletin, vol. 49, 75 p., 25 pls. Waterhouse, J.B., 1987: Late Palaeozoic Mollusca and correlation from the south-east Bowen Basin, East Australia. Palaeontographica, Pal. A, vol. 198, p. 129- 233, pls. 1-14. Yancey, T.E., 1985: Bivalvia of the H.S. Lee Formation (Permian) of Malaysia. Journal of Palaeontology, vol. 59, p. 1286-1297. Zhang, R., 1977 : Class Bivalvia. In, Hubei Geological Insti- tute ed., Palaeontological Atlas of Central-South-China, Part 2, p. 470-533, pls. 189-202. Geological Press. (in Chinese) Zhang, Y., 1981: Late Permian bivalves from Yunjia of Jahe, Hunan Province. Acta Palaeontologia Sinica, Vol. 20, no. 8, p. 260-265. (in Chinese with English abstract) Paleontological Research, vol. 3, no. 1, pp. 18-28, 6 Figs., April 30, 1999 © by the Palaeontological Society of Japan An early Late Cretaceous mammal from Japan, with reconsideration of the evolution of tribosphenic molars TAKESHI SETOGUCHI', TAKEHISA TSUBAMOTO’, HAJIME HANAMURA?’”’ and KIICHIRO HACHIY A’ ‘Department of Geology and Mineralogy, Graduate School of Science, Kyoto University, Kitashirakawaoiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan ‘Department of Anatomy, School of Dentistry, Aichi-Gakuin University, 1-100 Kusumoto-cho, Chikusa-ku, Nagoya 464-8650, Japan Division of Oral Aging, Resarch Institute of Advance Dental Science, Aichi-Gakuin University, 1-100 Kusumoto-cho, Chikusa- ku, Nagoya 464-8650, Japan Received 4 July 1998 ; Revised manuscript accepted 18 March 1999 Abstract. The morphology of a mandibular fragment with a left lower molar discovered in the “Upper Formation” (upper Cenomanian-lower Turonian) of the Mifune Group in central Kyushu, southwestern Japan, suggests that this fossil should be assigned to a new species of Late Cretaceous mammal, Sorlestes mifunensis sp. nov. (Infraclass Eutheria ; Order Proteutheria ; Family Zhelestidae). S. mifunen- sis is the oldest zhelestid yet recorded. Some workers suggest that the Zhelestidae have a close affinity with ungulates. A detailed comparison between the lower molar of the new species and those of ungulates supports this suggestion. The comparison also suggests that the Zhelestidae have a closer affinity with ungulates than the Zalambdalestidae and other contemporary mammals, and that S. mifunen- sis has a relatively primitive character within the Zhelestidae. This comparison leads us to revise the diagnoses of the family Zhelestidae and of the genus Sorlestes. The unique character of the entoconid- hypoconulid twinning seen in the Zhelestidae was probably caused by the movement of the hypoconid (the presumed first single talonid cusp seen in the first therian Kuehneotherium) to the buccal side, far away from the other talonid cusps. This twinning pattern is distinct from the twinning pattern seen in marsupials. Key words: Japan, Late Cretaceous, Mesozoic mammal, Mifune Group, Sorlestes, tribosphenic molar Introduction It is generally believed that tribosphenic mammals first appeared around the Jurassic-Cretaceous boundary (Bown and Kraus, 1979; Kielan-Jaworowska et al, 1979b; Sigogneau-Russell, 1991). They are ancestors of the eu- therian and metatherian mammals which probably differ- entiated during the Neocomian (Early Cretaceous) (Kielan Jaworowska et al., 1979a ; Cifelli, 1993 ; Eaton, 1993 ; Wang et al., 1995). The eutherian orders radiated widely at the beginning of the Tertiary. However, recent fossil finds suggest that the eutherian orders may have originated and differentiated in the Late Cretaceous (Fox and Youzwyshyn, 1994 ; Archibald, 1996 ; Gheerbrant et al., 1996). Until 20 years ago there were only very few reports of tribosphenic mammals from the early Late Cretaceous (Cenomanian-Santonian). This situation has, however, changed and many such fossils are now known from this period (Cifelli and Eaton, 1987 ; Cifelli, 1993; Eaton, 1993 ; Nessov et al. 1994; Nessov et al., 1998). In particular, Nessov et al. (1994) report many early Late Cretaceous tribosphenic mammals from Middle Asia (Uzbekistan, Ka- zakhstan and Tajikistan). In the present study, we document a mammal fossil specimen, which was first reported by Setoguchi (1992), from the “Upper Formation” (upper Cenomanian-lower Turonian ; lower Upper Cretaceous) of the Mifune Group in central Kyushu, southwestern Japan. The specimen is a small mandibular fragment with a tribosphenic lower molar. The new find is significant because it is the only known example of a mammal fossil from the Late Cretaceous eastern coastal lowlands of the Asian Continent. The other Asian Late Cretaceous mammal fossils, in contrast, come from either inland deposits or deposits along the Tethys sea and the Late Cretaceous mammal from Japan 19 Turgai Strait of that time (Clemens et a/., 1979 ; Nessov et al., 1994). The tooth nomenclature used in this contribution is that of Bown and Kraus (1979) and Nessov et al. (1998). Geological setting The present fossil material was discovered in the “Upper Formation” of the Mifune Group, which is distributed in the Mifune Town area of Kumamoto Prefecture, central Kyushu, southwestern Japan (Figure 1). The Mifune Group unconfor- mably overlies green schist associated with serpentinite in the northern area, and the Upper Permian Mizukoshi Forma- tion in the southern area (Matsumoto, 1939). The Mifune Group is, in turn, unconformably overlain by the Upper Cretaceous Gankaizan Formation (Tamura and Tashiro, 1966). The Mifune Group is considered to be early Late Cretaceous in age (see below), and to have formed in a sedimentary basin situated on the east coastal margin of the Late Cretaceous Asian Continent. The Mifune Group has a total thickness of about 1,500 m and consists of “Basal”, “Lower” and “Upper” formations (Matsumoto, 1939). The lowermost or “Basal Formation” is dominated by conglomerate and very coarse-grained sand- stone (Matsumoto, 1939), yielding fresh-water bivalves, such as Trigonioides, (Tamura, 1979; Matsumoto et al., 1982). The middle or “Lower Formation” is dominated by sandstone and sandy mudstone (Matsumoto, 1939), yielding brackish- water and shallow-marine molluscan fossils, such as /nocer- amus concentricus costatus and Eucalycoceras sp. cf. E. spathi of middle Cenomanian age (Tamura and Matsumura, 1974; Tamura, 1979; Matsumoto et al., 1982). The upper- most or “Upper Formation” is dominated by red mudstone (Matsumoto, 1939), yielding non-marine bivalves (Tamura, 1979) and several vertebrate fossils, such as dinosaurs, pterosaur, and the present specimen (Tamura et al., 1991; Setoguchi, 1992 ; Okazaki and Kitamura, 1996). The Gankaizan Formation, which unconformably overlies the Mifune Group, consists of conglomerate, coarse-grained sandstone and red mudstone (Tamura and Tashiro, 1966 ; Matsumoto et al., 1982), yielding Inoceramus (Platyceramus) amakusensis, of lower Santonian age, in its upper part (Tamura and Tashiro, 1966 ; Matsumoto et al., 1982). The present fossil material comes from the upper part of the “Upper Formation” near the Amagimi Dam, Mifune Town (Figure 1). The stratum where the fossil was discovered AU NE OSSI Figure 1. Topographic map showing the fossil locality, near the Amagimi Dam, Mifune Town, Kumamoto Prefecture, Kyushu, southwestern Japan (a part of topographic map “Mifune”, 1 : 25,000 scale, Geographical Survey Institute of Japan). 20 Takeshi Setoguchi et al. Upper Formation (non-marine) Mifune Group (m., partly br.) non-m.) LL 5 a © a Basement Stratigraphy | T.(m)| Lithology Fossils Inoogramus (Platyceramus) amakusenss ———® Lower Santonian Sorlestes (KUJM 95002), Piicatounio, Gyraulus, Pterodactyloidea, fam., gen. and sp. undetermined Siragimelania Nipponicorbula mashikensis Eucalycoceras sp. cf. E. spathh ——?® Middle Cenomanian Acanthotrigonia, Inoceramus, Septifer, Turritella Matsumotoa, Brachidontes, Crassostrea, Eomiodon, Tetoria, Pulsides ?Megalosauridae gen. et sp. indet. Nipponicorbula mashikensis Siragimelania Trigonioides, Plicatounio Figure 2. Stratigraphy of the Cretaceous deposits in the south of Kumamoto City, Kyushu, Japan (modified from Matsumoto, 1939 ; Tamura and Tashiro, 1966 ; Matsumoto et al., 1982 ; Tamura et al., 1991; Hasegawa et al. 1992 ; Okazaki and Kitamura, 1996). ss., sandstone ; cg., conglomerate. consists of coarse-grained sandstone. The age of the “Upper Formation” is considered to be late Cenomanian to early Turonian on the basis of the ages of the Lower Formation and the Gankaizan Formation. A synthetic scheme of the stratigraphy of the Mifune Group is shown in Figure 2. Systematic paleontology Class Mammalia Linnaeus, 1758 Infraclass Eutheria Gill, 1872 Order Proteutheria (Romer, 1966) Butler, 1972 Family Zhelestidae (Nessov, 1985) Nessov, 1990 Revised diagnosis.—The upper and lower molars are typical tribosphenic types. The protocone is large and mesiodistally expanded. The stylar shelf is relatively narrow, but the parastylar region is wide and expanded mesially bearing two cusps. A small paraconid is displaced relatively lingually and relatively close to the metaconid. Compared with other proteutherians, the trigonid height is lower relative to talonid height. The talonid is about as wide as the trigonid and mesiodistally longer and lower than the trigonid. Abbreviations : m., marine; br., brackish; T., thickness ; ms., mudstone ; The talonid basin is deep and open lingually, so that the deepest part of the talonid basin is situated at its lingual margin. The entoconid and hypoconulid are markedly close to one another, and are quite clearly separated from the hypoconid. The upper and lower last premolars are premolariform (sensu Krishtalka, 1976), but the upper one has a incipient metacone. In occlusal view, the upper one is somewhat mesiodistally constricted between the paracone and the protocone. Genus Sorlestes Nessov, 1985 Type species.—Sorlestes budan Nessov, 1985. Included species.—S. budan Nessov, 1985; S. kara Nes- sov, 1993; S. mifunensis sp. nov. Revised diagnosis.—The paraconid is not strongly appres- sed to the metaconid. The protoconid is larger than in Aspanlestes (Zhelestidae). The entoconid is very markedly close to the hypoconulid (entoconid-hypoconulid twinning), and both are located at the distolingual corner of the talonid, opposite the hypoconid which is located at the distobuccal corner. The cristid obliqua extends just below the notch of Late Cretaceous mammal from Japan the protocristid between the protoconid and the metaconid. Sorlestes mifunensis sp. nov. Figure 3 Holotype.—KUJM 95002, a left mandibular fragment with a molar. (KUJM means Kyoto University, Japan, Mesozoic) Hypodigm.—The type specimen only. Etymology.—Named after Mifune Town, where the type specimen was discovered. Repository.—Department of Geology and Mineralogy, Division of Earth and Planetary Sciences, Graduate School of [59] Science, Kyoto University, Japan. Locality.—Lat. 32°44’09” N ; Long. 130°50’32” E: Loc. 1 of Tamura et al. (1991, fig. 1; Figure 1), near the Amagimi Dam, Mifune Town, Kumamoto Prefecture, Kyushu, southwestern Japan. Horizon. —Upper part of the “Upper Formation”, Mifune Group (Figure 2). Age.—Late Cenomanian to early Turonian ; Late Cretaceous. Diagnosis.— The lower molar of S. mifunensis is almost as large as S. budan, and larger than S. kara. Compared to S. budan, the paraconid is less appressed to the metaconid, and the entoconid and hypoconulid are closer together. Figure 3. Sorlestes mifunensis sp. nov., KUJM 95002, holotype. A, A’, occlusal view (stereophotographic pair). B, lingual view. C, buccal view. D, D’, occlusal view of the preserved molar (stereophotographic pair). Scale bars=2 mm (left scale corresponds to A, A’, B, C, right scale corresponds to D, D’). 22 Takeshi Setoguchi et al. Description —The type specimen (KUJM 95002) is a frag- mentary left mandible with a molar. The preserved part of the mandibular ramus is about 8 mm in length, and about 4 mm in height and about 2 mm in width below the preserved molar. Immediately mesial to the molar, there is a broken root, which is circular and not compressed anteroposteriorly in occlusal view (Figures 3-A, A’). Immediately distal to the molar, there is a broken alveolus. Mental foramen could not be identified in KUJM 95002. The protoconid of the preserved molar is much larger and higher than the metaconid, and leans somewhat lingually. The metaconid is situated just lingual to the protoconid. Although badly broken at the base, it is clear that the paraconid is near the anteroposterior midline, and less anteriorly appressed than in S. budan. There is no crest joining the paraconid with the metaconid. A distinct precin- gulid runs downward from the mesiobuccal base of the paracristid notch, disappearing at the buccal base of the protoconid. The posterior trigonid wall is almost vertical, and nearly perpendicular to the mandibular extension. The talonid is longer than wide. It is longer than, as wide as, and roughly half as tall as the trigonid. The hypoconid and entoconid are almost the same height, and somewhat higher than the hypoconulid. The hypoconulid is only very slightly projected posteriorly. The entoconid and hypoconulid are closer together than in S. budan, and are located at the distolingual corner of the talonid. A very weak postcingulid runs down buccally from the hypoconulid, disappearing at the buccal base of the hypoconid. The deepest part of the vi AP > k TALL % TRIL y I TRIW Figure 4. Orientations of the measurements of lower molars (modified from Nessov et a/., 1994). Buccal to top of page ; anterior to right. Abbreviations are shown in Table 1. Table 1. sp. nov. talonid basin is situated at its lingual margin, so that the deep talonid basin is open lingually, and inclined lingually as a whole. The cristid obliqua originates directly below the notch between the protoconid and the metaconid, and is much higher than the entocristid. The hypoflexid is well- formed and deep. Wear facets can be observed from the tip of the protoconid to the tip of the metaconid through the proto- cristid. The tips of the hypoconid, hypoconulid and entoconid are slightly worn. The talonid basin is also worn (although the effects of secondary erosion are difficult to assess), which forms a U-shaped “wear facet”. Dental measurements are given in Table 1 and Figure 4. Discussion Identification of the present lower molar The tooth class of the molar preserved in KUJM 95002 can be identified as M., because the trigonid is as wide as the talonid which is the same as on M, of S. budan. The possibility that it should be identified as M, cannot, however, be immediately excluded. As Lillegraven (1976) pointed out, it is a usual therian condition that the paraconid is most buccally set on M, and becomes progressively more lingual on M.-M;. Furthermore, Cretaceous eutherians character- istically have a protoconid that leans somewhat more lin- gually on M, than that on M,, so the distance between the tip of the protoconid and that of the metaconid in occlusal view is shorter on M, than that on M,. These characters are also observed in the zhelestid Aspanlestes (Nessov et al., 1994, pl. 4, fig. 1). KUJM 95002 shows a combination of these M, characters. In either case, KUJM 95002 and S. budan clearly have distinct lower molar structures (see diagnosis of S. mifunen- sis). S. kara, another species of Sorlestes, has much smaller molar size than KUJM 95002. We, therefore, consider KUJM 95002 to be a new species of Sorlestes. Phyletic position of Sorlestes mifunensis Phylogenetic relationships of the Zhelestidae have been discussed by various workers (Figure 5). Lillegraven (1976) described Gallolestes, which was subsequently classified as belonging to the Zhelestidae by Nessov et al. (1994), based on the lower molar morphology. Lillegraven (1976) favors eutherian affinities for Gallolestes, and points out the similar- ities between Gallolestes and hyopsodontid condylarths. Butler (1977), however, points out that Gallolestes shares some derived characters of the lower molars with Zalamb- dalestes (Proteutheria; Zalambdalestidae) and with Pur- gatorius (Primatomorpha), and he doesn't exclude the possi- Measurements (in mm) of the preserved molars of the type specimens of Sorlestes mifunensis The measurements are oriented as shown in Nessov et al. (1994, fig.1; see Figure 4). Abbreviations : AP, anteroposterior length; TRIL, trigonid length; TALL, talonid length; TRIW, trigonid widt! ; TALW, talonid width. PTS Er [mm] AP TRIL TALL TRIW TALW KUJM 95002 (S. mifunensis) left lower molar (M, or M.) 1.15 1.45 1.75 | 1.70 | | | Late Cretaceous mammal from Japan 23 Nessov (1985) Butler (1990) : based on the|/based on the Pt EME Kennalestidae Kennalestes Sorlestes Zhelestes Zhelestes Aspanlestes Taslestes Mixotheridia Gallolestes Pe Coreundulates’) close to ungulates Family u Sorlestes Aspanlestes close to Taslestes Zalambdalestidae ? Gallolestes Zalambdalestidae Nessov et al. (1994) Archibald (1996) & Nessov et al. (1998) mainly based on the morphology of the lower molars mainly based on the morphology of Proteutheria the upper molars Kennalestidae Mixotheridia Kennalestidae ("preungulates") Zalambdalestidae Zhelestidae Zhelestes Sorlestes Ungulato! Aspanlestes Zhelestidae Taslestes Ungulata Gallolestes Zalambdalestidae Figure 5. The classifications and phylogenetic relationships used in recent studies for the Zhelestidae. bility of a relationship between Gallolestes and Protun- gulatum (Condylarthra). Clemens (1980) concludes that Gallolestes is possibly a representative of another lineage of metatherian-eutherian grade of dental evolution that cannot be assigned to either the Eutheria and Metatheria. Based on the lower molar morphology, Nessov (1985) suggests that Tas/estes, Aspanlestes, Sorlestes and Gal- lolestes should be combined in the same taxonomic group, a group which was subsequently classified as belonging to the Zhelestidae in Nessov et al. (1994). Nessov (1985) proposed a new suborder Mixotheridia (Proteutheria) includ- ing both the above genera and the Zalambdalestidae, and suggested that this suborder was related to condylarths. In the same paper, he described a new genus Zhelestes, based on the upper dentition. He classified it into the new sub- family Zhelestinae (Proteutheria ; Kennalestidae), and at this time didn't include it in the Mixotheridia. Later, he raised this subfamily to the family level (Nessov, 1990). Butler (1990) points out that the zalambdalestids differ from Aspan- lestes, Sorlestes and Gallolestes in some molar features, suggesting that relationships of these genera to zalamb- dalestids is not impossible, but it needs to be substantiated. He also considers that Zhelestes might be an earlier repre- sentative of condylarths. According to Nessov et al. (1994), the Zhelestidae include Gallolestes, Taslestes, Aspanlestes and Sorlestes, and these are all included in the suborder Mixotheridia along with the Zalambdalestidae. They con- sider the Mixotheridia (both the Zhelestidae and the Zalamb- dalestidae) to be “preungulates”. In contrast, based mainly on the upper molars morphology, Archibald (1996) and Nessov et al. (1998) consider that the Zhelestidae are sister groups of ungulates, and the Zalambdalestidae are only distantly related to them. In this paper, we follow the suggestions of Archibald (1996) and Nessov et al. (1998). The reasons for our preference are briefly summarized below. On the basis of the lower molar structure, Nessov et dl. (1994) claimed that both the Zhelestidae and the Zalamb- dalestidae are closely related to ungulates. However, the two families show the following differences: (1) The Zhe- lestidae have more low-crowned lower molars with a trigonid that is less elevated to the talonid (Butler, 1990). (2) The paraconid and metaconid in the Zhelestidae are less closely appressed than in the Zalambdalestidae. (3) The Zhe- lestidae have a lingually open talonid, whereas the talonid is lingually closed in the Zalambdalestidae (see Kielan-Jawor- owska, 1984, pl. 14,15). In these features, the Zhelestidae are morphologically more similar to early ungulates than to the Zalambdalestidae. Most early ungulates (for instance, Protungulatum, Diacodexis, and so on) share the diagnostic characteristics of zhelestids, that is, the high, large, wide and lingually open talonid with the hypoconulid situated markedly close to the entoconid, and the rather lingually displaced paraconid with some appression to the metaconid (see McKenna, 1960, figs. 52, 53, 56, 57 ; Archibald, 1982, figs. 56, 60; Estravis and Russell, 1989, pl.1; Rose, 1996, fig. 1). This combination of characteristics is not seen in any other contemporary mammal. For example, in Purgatorius, an early primatomorphan, the talonid is large, wide and high, but is Closed lingually with the hypoconulid situated centrally (see Clemens, 1974, fig.2; Buckley, 1997, fig.1). In Gypsonictops, a Late Cretaceous insectivore, the talonid is large, wide and somewhat lingually open. However, the hypoconulid is centrally situated, and the paraconid is situ- ated rather centrally than lingually (see Clemens, 1973, figs. 1,4; Cifelli, 1990, fig. 2). Based mainly on an analysis of upper molar morphology, Archibald (1996) and Nessov et al. (1998) suggest that the Zalambdalestidae does not have a close affinity with un- gulates. Similarly, a study of lower molar morphology indi- cates that the Zhelestidae most closely resemble early ungulates. The lingually closed talonid in the Zalambaa- 24 Takeshi Setoguchi et al. lestidae, which is shared by many other eutherians, may be an apomorphic character which zhelestids and early un- gulates do not posses (see below). This would imply that the Zalambdalestidae should be excluded from a very close relationship with ungulates. In support of this idea, some workers (Van Valen, 1964; McKenna, 1975; Stucky and McKenna, 1993; Archibald, 1996) consider the Zalambda- lestidae to be more closely related to Anagale and rabbits. Compared with the Zhelestidae, early ungulates have a relatively high talonid with robust cusps on the lower molars. Compared to the other representatives of the Zhelestidae, Sorlestes mifunensis shows a primitive characteristic in that the paraconid is less appressed to the metaconid. Nessov (1993) created a new family Kulbeckiidae (consist- ing of a single new genus Kulbeckia) within the Mixotheridia. In the Kulbeckiidae, the hypoconulid is markedly close to the entoconid, and the paraconid is lingually situated with appression to the metaconid, similar to the Zhelestidae. Unfortunately, it is not clear whether the talonid is open or not in the Kulbeckiidae, so it is difficult to discuss any possible relationship between the Zhelestidae, Kulbeckiidae and other mammals. Evolution of tribosphenic molars The most characteristic feature of Sorlestes mifunensis is the lower molar with the hypoconulid situated markedly close to the entoconid, quite clearly opposed to the hypoconid. This twinning pattern is rarely seen in other Cretaceous eutherians, in which the hypoconulid is centrally-located between the hypoconid and the entoconid. The recognition of this character prompted us to reconsider the evolution of the talonid cusps. It seems that the talonid cusps devel- oped along with the occluding upper tooth and the adjacent lower tooth. 1. First cusp formed in the talonid of Kuehneotherium, the first therian mammal: The earliest therian mammal, Kuehneotherium, had already appeared by the Norian (Late Triassic) (Fraser et al., 1985). In the lower molars of Kueh- neotherium, the tallest and largest Cusp can be recognized as homologous with the protoconid of the later tribosphenic molars. The other two cusps, which are situated mesiolin- gually and distolingually from the protoconid, can likewise be identified as equivalents of the paraconid and metaconid, respectively (Kermack et a/., 1968). These homologies of the trigonid Cusps are now not really in debate (Slaughter, 1971). In the lower molars of Kuehneotherium, there is, however, a unicuspid distal heel or talonid, posterior to the trigonid (Kermack et al., 1968, fig. 3). The homology of this cusp has been discussed by several workers (Slaughter, 1971; Clemens and Lillegraven, 1986), and the two main opinions are that it corresponds to either the hypoconid or hypoconulid. Mills (1967) used the occlusal relationship between the upper and lower molars to propose that the single talonid cusp of Jurassic pantotheres corresponds to the hypoconid on the basis of the occlusal relationship between the upper and lower molars. The same conclusion was also reached by Freeman (1979) and Prothero (1981). In contrast, Kermack (1967) interpreted the single talonid cusp in Welsh pantothere (Kuehneotherium) as the hypoconulid on the basis of the relationship between the talonid and its following tooth. Crompton (1971), Slaughter (1971) and Butler (1978) also correlated this cusp with the hypoconulid, although the latter didn't completely exclude the possibility that it could repre- sent the hypoconid. The next stage in evolution toward the tribosphenic molar is seen in Amphitherium or Palaeoxonodon, whose talonid extends distobuccally from the base of the metaconid and bears a large single cusp at its distobuccal margin (Simpson, 1928, fig. 38 ; Freeman, 1979, pls. 16,17). In Palaeoxonodon, there is a small cuspule at the approximate median point of the oblique crest which links the metaconid and a large single talonid cusp (Freeman, 1979). Further development is seen in Peramus. In this genus the talonid bears two or three cusps, identified as the hypoconid, hypoconulid and entoconid of the tribosphenic molar (Clemens and Mills, 1971; Clemens and Lillegraven, 1986). The talonid basin is not fully basined and is open lingually (Clemens and Mills, 1971, pl. 3). By comparing the molar morphology of the animal mentioned above with later tribosphenic mammals, we consider that the single talonid cusp seen in Kuehneother- jum corresponds to the hypoconid, as proposed by Mills (1967). This suggestion is also supported by the following arguments. (1) We would like to stress the occlusal relation- ship between the upper main cusp (paracone) and the first talonid cusp. The paracone is the largest cusp in the upper molar and is functionally very important for masticating foods. We, therefore, propose that the occlusal relationship between the paracone and the single talonid cusp, as well as between the paracone and the protoconid, is likely to be maintained in the therians. (2) In Amphitherium or Palae- oxonodon, the talonid extends distobuccally from the base of the metaconid and bears a large single cusp at its distobuc- cal margin, where the hypoconid of the tribosphenic molar is situated. (3) We propose, furthermore, that the groove separating the hypoconid and the hypoconulid in tribos- phenic molars is also significant. This groove is deeper and stronger than the groove separating the hypoconulid and the entoconid, so the hypoconulid and entoconid are likely to be related more closely to each other than to the hypoconid. (4) Freeman (1979) stated that in certain specimens of Palaeoxonodon there is an incipient development of the entoconid and hypoconulid in addition to the large talonid cusp situated distobuccally. We, therefore, propose the following sequential develop- ment. The first talonid cusp seen in Kuehneotherium corre- sponds to the hypoconid, and the entoconid and hypoconulid appeared at some later stage, being more closely related to each other than to the hypoconid. 2. Entoconid-hypoconulid twinning: The primitive talonid for a tribosphenic molar envisaged by most workers is basined and lingually opened with a relatively large hypoconid, smaller hypoconulid and in some cases also an entoconid (Clemens and Lillegraven, 1986; Szalay, 1994). Examination of Early Cretaceous tribosphenic mammals suggests that the roughly centrally-placed hypoconulid Late Cretaceous mammal from Japan between the hypoconid and the entoconid may also be a primitive Characteristic. In Late Cretaceous mammals, the lower molars of many eutherians have a centrally-placed hypoconulid. In con- trast, the molars of contemporary marsupials have a hypoconulid twinned with an entoconid. In this respect the molars of the eutherian Zhelestidae resemble those of marsupials. However, the twinning in the Zhelestidae is clearly distinct from that in marsupials (Figure 6). In marsupials, the hypoconulid is distolingually displaced compared to the Zhelestidae. The twinning pattern seen in the Zhelestidae is associated with a primitive-type talonid as seen in the tribosphenic pattern. This association suggests that the twinning seen in the Zhelestidae is more primitive than in marsupials. The twinning pattern seen in the Zhelestidae is likely to have been caused by the movement of the hypoconid to the buccal side far away from the other talonid cusps, corresponding to the expansion of the protocone of the upper molars (Archibald, 1996 ; Nessov et al., 1998). The twinning pattern seen in marsupials is more likely to be a secondary feature (Cifelli, 1993), and could be functionally related to the early trend of the enlargement of the metacone and reduction of the paracone in this group (Clemens and Lillegraven, 1986). The entoconid-hypoconulid twinning is also related to the position of the paraconid of the posterior molar. This is because the paraconid fits into the groove between the hypoconulid and the entoconid of the anterior tooth. In many eutherians, the paraconid is situated centrally, Zhelestidae Other eutherians and ungulates sone hypoconulid Nw Nn because the hypoconulid of the anterior tooth is centrally- placed between the hypoconid and the entoconid, and the groove between the hypoconulid and the entoconid is situated more buccally. In the Zhelestidae, the paraconid is situated more lingually than centrally, because the hypoconulid is situated lingually and twinned with the entoconid, and the groove between the two cusps is situated more lingually than centrally. In marsupials, the paraconid is situated more mesiolingually than in eutherians (include the Zhelestidae), because the hypoconulid of the anterior tooth is situated more distolingually and twinned with the entoconid, and the groove between the two cusps is situated far more distolingually. As mentioned above, the lingually open talonid with a hypoconulid markedly close to the entoconid as seen in the Zhelestidae is probably a reflection of the primitive state. This condition is also seen in early eutherian like Proken- nalestes (Kielan-Jaworowska and Dashzeveg, 1989, figs. 26, 27), but not seen in early metatherian, Kokopellia (Cifelli, 1998, fig. 1). Co-evolution of mammals and plants The age from the Albian to the Cenomanian was a very important period for the mammalian evolution. At this time the flora underwent a change from one dominated by ferns and gymnosperms to one with abundant angiosperms. Flowering angiosperms appeared at the beginning of the Cretaceous, and very rapidly became a major plant group (Crane, 1987 ; Collinson, 1990). Angiosperms have leaves, Marsupials protoconid entoconid paraconid metaconid deepest part of the talonid basin Primitive tribosphenic pattern buccal distal Eu mesial lingual O O ee) Figure 6. Comparisons of the lower molar patterns of tribosphenic mammals (occlusal view of the left lower molars). 26 Takeshi Setoguchi et al. flowers, fruit, pollen and honey. In other words, these plants have foods with high nutritive value. It was for this reason that insects began to evolve explosively at this time. It follows, therefore, that insectivorous mammals, whose staple foods were insects and/or larvae of insects, also began to increase in numbers and diversity. The mammals who began to diversify and radiate in this way are the Cretaceous tribosphenic mammals. The period when the Mifune Group was deposited is the very period when angiosperms had become a major plant group, and when insectivorous mam- mals like Sorlestes evolved rapidly. Conclusions Morphological studies of the mammalian remain discov- ered from the lower Upper Cretaceous Mifune Group in central Kyushu, southwestern Japan suggest that it should be assigned to a new species of the genus Sorlestes (Order Proteutheria ; Family Zhelestidae), and is here named S. mifunensis. The lower molars of the Zhelestidae exhibit a series of ungulate-like characteristics. It suggests that the Zhe- lestidae and early ungulates are far more closely related to each other than to the Zalambdalestidae and other mam- mals. The twinning pattern of the hypoconulid and entoconid in the Zhelestidae, including Sorlestes mifunensis, shows a more primitive state than that of metatherians and most of the other eutherians. Sorlestes mifunensis is the oldest known zhelestid yet recorded, and suggests that the origin of ungulates perhaps goes back even further to the early Late Cretaceous, or at least, that mammals having ungulate-like characters had already been differentiated by the late Cenomanian to early Turonian. The find of Sorlestes mifunensis also indicates that zhelestid existed not only in western Asia but also on the coastal plain of eastern Asia. Acknowledgments We are grateful to Kazuhiro Koyasu of Aichi-Gakuin University, who donated the specimen to Kyoto University. Our thanks also go to Naoki Ikegami of Mifune Board of Education, who gave us facilities in our field work. Thanks are also due to Hidetoshi Kamiya of Kyoto University, who gave the specimen number to the present material. We would like to express our sincere gratitude to Masanaru Takai of Kyoto University Primate Research Institute for his critical reading of the manuscript and taking the photographs of the specimen, to Naoki Kohno of National Science Museum and Simon R. Wallis of Kyoto University for their critical reading of the manuscript, and to Haruyoshi Maeda of Kyoto University for his advice about the construction of the manuscript. This manuscript was improved following con- structive reviews by two anonymous referees. This research was partly supported by Grant-in-Aid for JSPS Fellows from the Ministry of Education, Science, Sports and Culture of Japan to Takehisa Tsubamoto (No. 9714). References Archibald, J.D., 1982: A study of Mammalia and geology across the Cretaceous-Tertiary boundary in Garfield County, Montana. University of California Publications in Geological Sciences, vol. 122, xvi+286 p. Archibald, J.D., 1996 : Fossil evidence for a Late Cretaceous origin of “hoofed” mammals. 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Paleontological Research, vol. 3, no. 1, pp. 29-35, 3 Figs., April 30, 1999 © by the Palaeontological Society of Japan A new cheirolepidiaceous conifer from the Lower Cretaceous (Albian) of Hokkaido, Japan KEN'ICHI SAIKI Department of Plant Science, Natural History Museum and Institute, Chiba 955-2, Aoba, Chuo-ku, Chiba 260-8682, Japan Received 8 August 1998 ; Revised manuscript accepted 28 November 1998 Abstract. A new fossil conifer, Pseudofrenelopsis glabra sp. nov., (Cheirolepidiaceae) is described based on a single specimen obtained from the Lower Cretaceous Yezo Group (Albian) of Hokkaido, Japan. The new species is characterized by cuticle possessing thin periclinal walls, a well-developed hypodermis, and absence of trichomes on internode and outer leaf surface. Recently, the author described Frenelopsis pombetsuensis from the Lower Cretaceous Yezo Group (Albian) of Hokkaido. The family Cheiro- lepidiaceae is a diagnostic taxon of the Ryoseki-type element that is reported only from the Ryoseki- and the Mixed-type floras. Thus Pseudofrenelopsis glabrais the second evidence of the Ryoseki-type element from Hokkaido. Key words: Albian, conifer, Hokkaido, Middle Yezo Group, Pseudofrenelopsis glabra, Ryoseki-type floras. Introduction Jurassic and Early Cretaceous floras in eastern Eurasia have been classified by Kimura (1980, 1987) and Ohana and Kimura (1995) into three characteristic floras, the Ryoseki- and the Tetori-type floras, and the Mixed-type floras com- prising elements of both the Ryoseki- and the Tetori-type floras. According to these authors, the Ryoseki-type floras grew under tropical to subtropical conditions with an annual long arid season, while the Tetori-type floras grew under temperate and moderately humid conditions. The genus Pseudofrenelopsis belongs to the extinct conifer family Cheirolepidiaceae. Although this family is a dominant group of Mesozoic conifers, its closer affinity remain equivocal. The members of the family have various kinds of shoot morphology ranging from Brachyphyllum- Pagiophyllum-type shoots bearing scale leaves to Frenelop- sis-Pseudofrenelopsis-type cylindrical segmented shoots bearing minute leaves. The single most reliable character of this family is possession of the pollen of the genus Classopollis Pflug (Watson, 1988). Although the plants yield- ing fossil remains attributed to the genus Pseudofrenelopsis were widely distributed during the Early Cretaceous (Ber- riasian-Albian) of North America, Europe, North Africa and Asia, they were apparently restricted to the Cretaceous (Table 1). The frenelopsids, which include the genus Pseudo- frenelopsis and the closely related genus Frenelopsis, have been used as indicator taxa of tropical to subtropical arid climate (Alvin, 1982). In east Asia the occurrence of the frenelopsids in fossil floras is restricted to the Ryoseki- and the Mixed-type floras. Although Frenelopsis is known from the Ryoseki-type floras of the Upper Jurassic to Lower Cretaceous in Japan, fossil remains assigned to Pseudo- frenelopsis have not been reported yet. In the present paper, the remains of shoot and associated cuticular fea- tures of Pseudofrenelopsis from Japan are described. Mikasa City Museum Katsurazawa Lake Xn | Figure 1. Map of Hokkaido, Japan showing the location of the Pombetsu Valley. Ken'ichi Saiki 30 Cheirolepidiaceous conifer from Lower Cretaceous of Hokkaido 31 Material and Methods Material—A compressed conifer shoot was found in the Pombetsu Valley about 60 km northeast of Sapporo (Figure 1). The specimen was obtained from the mudstone bed of the so-called “Main part of Middle Yezo Group”. The locality is situated between Matsumoto's outcrops Ik 2025 and 2031, from where the Albian ammonite Ammonoceratites yezoensis Yabe has been reported (Matsumoto, 1965, fig. 3). Methods.—Fossil remains were immersed in Schulze’s solution followed by diluted NaOH. The cuticle was mounted in Eukitt for light microscopy. For SEM observa- tion, cuticles were coated with Pt-Pd in a Hitachi E-1030 ion sputter and photographed with Hitachi S-800. All specimens used in this study are deposited in the Mikasa City Museum (MCM), Ikushumbets-nishikicho, Mi- kasa, Hokkaido. Systematic description Order Coniferales Family Cheirolepidiaceae Takhtajan, 1963 Genus Pseudofrenelopsis Nathorst, 1893 Remarks of the genus.—The diagnosis originally based only on the type species was emended by Watson (1977) after studying specimens of Frenelopsis varians Fontaine, which is now placed in this genus. Recently, Srinivasan (1995) emended the diagnosis of Pseudofrenelopsis based on new morphological characters of Puddledock material. Srinivasan's concept is followed here. Pseudofrenelopsis glabra sp. nov. Figures 2A-H, 3A-I Material.—Holotype, MCM-PO30 Horizon.—Main part of the Middle Yezo Group (Albian). Type locality —Pombetsu Valley, Mikasa, Hokkaido (Figure 1; ca. 4316°31”N, 141°59'20”E). The locality is about 80 m south of Matsumoto’s (1965) outcrop Ik 2031. Diagnosis.—Segmented shoot bears a simple spiral of leaves, each leaf encircling the stem. Leaf margin having hairs ; outer surface of both abaxial and adaxial leaf cuticle smooth, without trichomes. Internode cuticle well devel- oped. Outer surface of cuticle smooth, nonpapillate. Stomata arranged in longitudinal rows. Stomatal complex consisting of a pair of guard cells and 7-9 subsidiary cells. Guard cells sunken below a ring of subsidiary cells with irregularly oriented apertures. Stomatal pit rounded in sur- face view. Outer surface of subsidiary cells forming a raised rim bounded by a deep groove around stomatal pit. A well developed cutinized hypodermis of thin-walled cells cover- ing most of the internal surface of the cuticle. Description.—A single compressed shoot was obtained (Figures 2A, B). The shoot is segmented, bearing a simple spiral of leaves. Each of the leaves encircles the stem. The internode is 6-9 mm long and 4 mm wide (Figures 2A, B). Triangular part of the leaf is up to 1.5 mm high at a node (Figures 2B, C; 3A). The leaf margin has hairs up to 40 um long (Figures 2E ; 3B, C). Outer surface of both abaxial and adaxial leaf cuticle is smooth, without trichomes (Figures 3B- D). The internode cuticle is well developed, about 8 um in total thickness. The cuticle consists of outer periclinal epidermal wall about 3 «m thick, anticlinal wall and thinly cutinized hypodermis (Figure 3E). No dorsiventrality is ob- served (Figure 2F). Stomata are about the same optical density as the rest of cuticle and are arranged in well marked longitudinal rows in 7-9 rows per mm. Each row of stomata is a single stoma wide. 70-100 per mm? in density. (Figures 2F, G; 3F, G). The bands of epidermal cells between the rows of stomata are 20-70 um (1-3 cells) wide, consist of longitudinally arranged epidermal cells. The epidermal cells are elongated rectangular to polygonal in shape, 25-50 um long and 10-25 um wide (Figures 2F,G; 3G). Outer surface of the cuticle is smooth, nonpapillate (Figure 3F). The stomatal complex is 80-120 um in diameter, consists of a pair of guard cells and 7-9 subsidiary cells (Figure 3G). The guard cells are 40-70 uum long and 10 ~m wide and are sunken below a ring of subsidiary cells. The aperture of the stoma is irregularly oriented (Figure 3G). The stomatal pit is about 30 um in diameter and is rounded in surface view (Figures 3F, H). Outer surface of the subsidiary cells forms a raised rim bounded by a deep groove around stomatal pit. Each of the subsidiary cells has a single papilla projecting into the stomatal pit (Figures 2H ; SF, H, |). A well developed cutinized hypodermis of thin-walled cells cover most of the internal surface of the cuticle except for the region immediately beneath each stomatal apparatus. The hypodermal cells are rectangular or polygonal under the stomatal zone and are axially elongate rectangular under the nonstomatal zone (Figures 3E, G). Discussion.—Due to the fragmentary nature of the fossil specimen the arrangement of the branch system of Pseudo- frenelopsis glabra is uncertain. External and cuticular observations of the specimen clearly indicate the absence of a groove or suture separating the basal cushions, as seen in living species of the Cupressaceae. Although the epidermal cells are clearly visible with light microscopy (Figure 2G), SEM microscopy of the inner surface of cuticle shows only hypodermis and stomatal complexes, Figure 2. Pseudofrenelopsis glabra sp. nov. (MCM-P030). holotype showing leaf margins (I). A: Holotype (MCM-P030). B: Middle region of the C, D: Opposite sides of the same shoot fragment showing the margin of a single leaf (I). E: Light microscope image of the leaf margin showing short hairs. region showing fold represented by central dark line, and cuticles of both sides of the compressed specimen. of stomata and epidermal cells show no siginificant difference on both sides of the cuticles. of cuticle from the internodal region showing longitudinally arranged stomata, light microscope. of stomata, focused through the stomatal pit showing the papillae. F: Light microscope image of cuticle from internodal Arrangement G: Light microscope image H: Light microscope image Scale bars=5 mm in A-D; 100 um in E-H. 10} D Ken’ichi Saiki Figure 3. SEM micrographs of Pseudofrenelopsis glabra sp. nov. cuticle (MCM-P0O30). A: Triangular free part of leaf. B: Edge of a leaf, showing marginal hairs and outer surface of abaxial leaf cuticle. C: Enlarged photo of 3B showing the short marginal hairs and smooth outer surface of the abaxial (ab) and adaxial (ad) leaf cuticle. D: Surface view of adaxial leaf cuticle (ad) and inner view of cuticle from the internodal region (i). E: Section of cuticle showing cutinized epidermis (c) and hypodermis (h). F: Outer view of cuticle from the internodal region showing mouth of stomatal pit. G: Cuticle from the internodal region showing longitudinally arranged stomatal complexes. Inner view of stomatal complexes showing the guard cells (g), and subsidiary cells (s). H: Outer view of a stoma showing the rounded mouth of the stomatal pit with papillae. 1: Section of stoma showing guard cells (g), and papillae in throat of stoma (p). Scale bars=500 um in A, B; 50 um in C, D, F-H; 10 um in E, I. 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ARSOU euou w7/ 002 0} dn wr QOL sawoyol} ur O’GpL 0} dn surey WW Q'} SoA wu 0'2-0'1 wu 67-01 ‘aou “ds eıgey6 ‘d euensioyjeu ‘q SIsuaueysiay ‘qd — SMOJ PSUIJEP [JOM 9u0U auou wit G-€ sırey Jnoyym sırey NOUJIM ww z euou WW ÿ-G'e ww 9-G SMOJ pauyap |jem euou ee||ided ete] um wr/(gZ-)01-9'1(-9) surey 1noyym Ajjeuwlou sirey 1NOyuMm ww Z auou WLU g'g-& WLW OL-G'G sisuazjejep ‘d SMOJ jeulpnyBuo| euou jussaud Ajjensn wi! G'2-G juesaid sirey uw” O8 0} dn sie WLU GL auou WWW G'/-€ wu LLG esoyided ‘d SMOJ peuljep [JOM paziulynd em surey Buo Alan 0} euou ur (€ juasaid surey uw” 08 0} dn sırey WW Z UO} ‚uedo, SOS UI > WLU | esoweJsao4ed ‘4 PES, ul peueyeos suolysno sseq-jes| ,uado,, ul uw” 08 0} dn ur” OLL-OS juasaid suey uw” 09 0} dn surey WW G'| auou ww J-¢ wu /1-Gl SUBLIEA ‘d ‘saioads payejaı pue ‘aou ‘ds eiqe{6 sIsdojauaopnesd Jo saorawoydiow antpereduio9 Loge. jueusBueie |eYEWO}S sıwlspodAy paziuijing SI89 jewıopıdo uo SIIEU JO SAWOYOH | SSaUMOIU} a|o1n9 apouss}u| jee] JO aoeNs jeixepe uo siley JO SAWOYOU | ulBuew yea yes] 99 jo u}Bus] WNWIXeIN def 10 aunyns Jo aouasald UIPIM SpouIsqu] u}Bus| apousa}u| saloadg/ SiJoBIeUN 34 Ken'ichi Saiki because the epidermal cells are covered by cutinized hypodermis (Figure 3G). Comparison.—Although the present specimen is fragmen- tary, both external and cuticular features of the specimen correspond well with the diagnosis of Pseudofrenelopsis Nathorst emended by Srinivasan (1995) in its segmented shoot bearing a simple spiral of leaves, smooth cylindrical internode, and guard cells sunken below ring of subsidiary cells. Among the species of Pseudofrenelopsis previously de- scribed, the European P. varians (Fontaine) Watson and American P. parceramosa (Fontaine) Watson differ from P. glabra in possessing an extremely thick cuticle and having trichomes on the adaxial surface of the leaf cuticle (Watson, 1977). Although various species of Pseudofrenelopsis have been reported from China, most are provided with brief descrip- tions (Zhou, 1995). Recently, Zhou (1995) reexamined and combined the Chinese Pseudofrenelopsis into the following three species : P. papillosa (Chow et Tsao) Zhou, P. dalatzen- sis (Chow et Tsao) Zhou, and P. heishanensis Zhou (Table 1). Pseudofrenelopsis glabra is similar to these Chinese species in possessing a thinner internode cuticle than the European and American species. Pseudofrenelopsis dalatzensis and P. heishanensis can be distinguished from P. glabra by the stellate rim of the stomatal pit and absence of hairs on their leaf margins. The shape of the cells, smooth periclinal walls, and thin anticlinal walls of the hypodermis of Pseudofrenelopsis glabra (Figures 3G, E) are very similar to the “epidermal cells” of Pseudofrenelopsis heishanensis described by Zhou (1995). However, detailed light and SEM microscopy of P. hei- shanensis is required prior to meaningful comparison of P. heishanensis and P. glabra. Pseudofrenelopsis papillosa, redescribed in detail by Zhou (1995), possesses the most similar cuticle to that of P. glabra in having hairs on the margin of the leaf, round stomatal pits, and a thin cuticle. These resemblances may indicate a close phylogenetic relationship between these two species. Pseudofrenelopsis glabra is however, clearly distinguished from P. papillosa by a smaller number of subsidiary cells and absence of trichomes on the outer surface of the leaf adaxial cuticle. Paleophytogeography.—Since Kimura (1961,1975) has divided the Late Jurassic-Early Cretaceous floras of Japan and its adjacent areas into the Ryoseki-type and the Tetori type floras, this paleophytogeographical distinction has been extended to East Asia with some modification, and the Mixed-type flora that consist predominantly of the Ryoseki type element and subordinate Tetori-type element was added (Kimura, 1980, 1987 ; Kimura and Ohana, 1992 ; Cao, 1994 ; Ohana and Kimura, 1995). Although the Mesozoic flora of Hokkaido is famous for its well preserved permineralized materials, the stratigraphic range of these materials is restricted to the Upper Cretaceous (Nishida, 1991). So far, the absence of Jurassic and Lower Cretaceous fossil plants from Hokkaido had prevented comparison of the Early Cretaceous flora of Hokkaido with the Ryoseki- and the Tetori-type floras. Recently, Saiki (1997) described Frenelopsis pombetsuensis, from the Lower Cretaceous Yezo Group (Albian) of Hokkaido. The family Cheirolepidiaceae is a diagnostic taxon of the Ryoseki-type element reported only from the Ryoseki- and the Mixed-type floras (Ohana and Kimura, 1995). Thus, Pseudofrenelopsis glabra is the second evidence of the presence of Ryoseki-type element from Hokkaido. Ohana and Kimura (1995) estimated that the Ryoseki-type floras flourished under tropical or subtropical conditions with an annual long arid season. Their idea is consistent with the thermophilous nature of frenelopsids proposed by Alvin (1982) based on the distribution of frenelopsids of the world and their possession of a thick cuticle. However, the two frenelopsids species from Hokkaido lack two of the xeromor- phic features observed in many other frenelopsids, namely, a thick cuticle and trichomes on the internode surface. The cuticle thickness of eight species listed in Alvin (1982) are 8- 110 um thick in their periclinal wall rather than 3 um and 3- 4 um thick as in Frenelopsis pombetsuensis and Pseudo- frenelopsis glabra respectively. The cuticular features of Frenelopsis pombetsuensis and Pseudofrenelopsis glabra may reflect the rather humid condition inferred for the Albian of Pombetsu, rather than the xeric conditions from other regions of the world where frenelopsids were distributed (Alvin, 1982). This assumption is consistent with recent palynological data indicating that the group inhabited a variety of ecological niches (Watson, 1988). Acknowledgments The author thanks T. Kimura, director of the Institute of Natural History, Tokyo, for his critical reading the manuscript and his helpful suggestions ; M. Futakami, |. Obata, M. Ma- tsukawa, Y. Taketani, M. Ito and H. Nagata for their encour- agement and helpful suggestions. Thanks are also extended to Ben A. LePage, University of Pennsylvania, for his kindness in critically reading the manuscript. This study was supported by the Ishikari River Local Head Office, Hokkaido Development Bureau. References cited Alvin, K.L., 1977 : The conifer Frenelopsis and Manica in the Cretaceous of Portugal. Palaeontology, vol. 20, p. 387- 404. Alvin, K.L., 1982 : Cheirolepidiaceae : Biology, structure and paleoecology, Review of Palaeobotany and Palynology, vol. 37, p. 71-98. Alvin, K.L., Spicer, R.A. and Watson, J., 1978: A Classopol- lis-containing male cone associated with Pseudo- frenelopsis. Palaeontology, vol. 21, p. 847-856. Cao, Z., 1994: Early Cretaceous floras in Circum-Pacific region of China. Cretaceous Research, vol. 15, p. 317- 332. Chow, T.Y. and Tsao, C.Y. 1977: On eight new species of conifers from the Cretaceous of East China with refer- ence to their taxonomic positiion and phylogenetic relationship. Acta Palaeontologica Sinica, vol. 16, no. 2, p. 165-181. (in Chinese with English summary) Kimura, T., 1961: Mesozoic plants from the Itoshiro Sub- Cheirolepidiaceous conifer from Lower Cretaceous of Hokkaido group, the Tetori Group, Central Honshu, Japan. part 2. Transactions and Proceedings of the Palaeontological Society of Japan, New Series, no. 41, p. 21-32. Kimura, T., 1975: Notes on the Early Cretaceous floras of Japan. Bulletin of the Tokyo Gakugei University, Series 4, vol. 27, p. 217-257. Kimura, T., 1980: The present status of the Mesozoic land floras of Japan. Professor Saburo Kanno Memorial Volume, p. 379-413. Tsukuba University. Kimura, T., 1987: Geographical distribution of Palaeozoic and Mesozoic plants in East and Southeast Asia. In, Taira, A. and Tashiro, M. eds., Historical Biogeography and Plate Tectonic Evolution of Japan and Eastern Asia, p. 135-200. Terrapub, Tokyo. Kimura, T. and Ohana, T., 1992: Cretaceous palaeobotany and phytogeography in Eastern Eurasia. Palaeontological Society of Korea, Special Publication, no. 1, p. 27-34. Matsumoto, T., 1965: A monograph of the Collignoni- ceratidae from Hokkaido, part1. Memoirs of the Fac- ulty of Science, Kyushu University, Series D, no. 16, p. 1-80. Nishida, H., 1991: Diversity and significance of Late Cretaceous permineralized plant remains from Hok- kaido, Japan. Botanical Magazine Tokyo, vol. 104, p. 253-273. Ohana, T. and Kimura, T., 1995: Late Mesozoic phytoge- ography in eastern Eurasia, with special reference to the ww in origin of angiosperms in time and site. Proceedings of 15th International Symposium of Kyungpook National University, p. 293-328. Saiki, K., 1997 : Frenelopsis pombetsuensis : a new cheiro- lepidiaceous conifer from the Lower Cretaceous (Albian) of Hokkaido, Japan. Paleontological Research, vol. 1, no. 2, p. 126-131. Srinivasan, V., 1995: Conifers from the Puddledock locality (Potomac Group, Early Cretaceous) in eastern North America. Review of Palaeobotany and Palynology, vol. 89, p. 257-286. Watson, J., 1977: Some lower Cretaceous conifers of the Cheirolepidiaceae from the U.S.A. and England. Palaeontology, vol. 19, p. 715-749. Watson, J., 1988: The Cheirolepidiaceae. In, Beck, C.B. ed., Origin and Evolution of Gymnosperms, p. 382-447. Columbia University Press, New York. Zhou, Z., 1995: On some Cretaceous pseudofrenelopsids with a brief review of cheirolepidiaceous conifers in China. Review of Palaeobotany and Palynology, vol. 84, p. 419-438. Zhou, Z. and Cao, Z., 1979: Some Cretaceous conifers from southern China and their stratigraphical significances. In, Institute of Vertebrate Palaeontology and Palaeoanthropology, and Nanjing Institute of Geology and Palaeontology, Academia Sinica eds, Mesozoic and Cenozoic Red Beds of Southern China, p. 218-222. Science Press, Beijing. Ikushumbets-nishikicho #4 5/$#H), Mikasa =*, Pombetsu #1] Paleontological Research, vol. 3, no. 1, pp. 36-40, 3 Figs., April 30, 1999 © by the Palaeontological Society of Japan The first record of Mesoturrilites (Ammonoidea) from Hokkaido (Studies of the Cretaceous ammonites from Hokkaido and Sakhalin — LXXxXill) TATSURO MATSUMOTO and AKITOSHI INOMA c/o Faculty of Science, Kyushu University, Fukuoka 812-8581, Japan 6-29-19 Daida, Setagaya, Tokyo 155-0033, Japan Received September 3 1998 ; Revised manuscript accepted 22 November 1998 Abstract. Several small specimens collected years ago by A.l. from a locality in the Soeushinai area of Hokkaido are now identified as Mesoturrilites boerssumensis (Schlüter, 1876). The species has been reported from the Lower Cenomanian of western and central Europe and western Asia. Our material is also referred to the Lower Cenomanian on the biostratigraphic evidence. This may be the first record of Mesoturrilites in the northern Pacific region. Key words : Cenomanian, geographic distribution, Hokkaido, Mesoturrilites, Pacific region, Turrilitidae Introduction A number of species belonging to Mariella, Pseud- helicoceras, Ostlingoceras, Neostlingoceras, Turrilites and Hypoturrilites of the family Turrilitidae [Ammonoidea] show worldwide distribution. Some of them occur fairly commonly in the Upper Albian and Cenomanian strata in Japan, although many of them are waiting for complete descriptions. In this paper a species of Mesoturrilites from Hokkaido is described. Stratigraphic setting The area concerned, called “Soeushinai’, was geologically mapped by Hashimoto et al. (1965) and has been recently reinvestigated by Nishida et al. (1996, 1997, 1998a, b). According to these authors, a thick series of strata called the Middle Yezo Subgroup of late Albian through Turonian age, is extensively exposed in this area. The subgroup is sub- divided into Members My1 to My8 in a revised scheme of Nishida et al. (1996, fig. 10). The specimens described below were contained in a transported nodule obtained by A.l. in 1959. That nodule was collected in the upper reaches of the Sanjussen-zawa, a tributary of the River Uryu. The nodule is interpreted as a derivative from Member Mys. This member consists primarily of mudstones which have sometimes fine-grained sands or sandy laminae and contain commonly calcareous nodules. Ammonoids occur fairly abundantly in Member My3 together with inoceramids and other mollusks. Some of them were described by Matsu- moto and Inoma (1975, 1991) and Inoma (1980) and also amply listed by Nishida et a/. (1996, 1997). The fauna forms the Assemblage Zone of Graysonites adkinsi, indicating the lower part of the Lower Cenomanian. The overlying Member My4 is composed of ill-sorted conglomerates in some parts and predominant sandstones with some mudstones and conglomerates in other parts. It is poor in fossils. The succeeding Member My5 consists mainly of mudstones which contain numerous inoceramids with some associated ammonoids, representing the rest of the Cenomanian. The Inoma’s locality, numbered Al-72803, is concisely indicated in a map by Matsumoto and Inoma (1975, fig. 2) and more precisely in Figure1. A fossiliferous nodule contains small specimens of Algericeras proratum (Coquand) and Euhystrichoceras cf. nicaisei (Coquand) besides those of Mesoturrilites described herein. At another locality, R7239p, about 70m NEE of AI-72803, Y. Kawashita and N. Egashira obtained another ammonite which is identified by T.M. with Gabbioceras yezoense Shigeta. The three ammonite species indicate an early Cenomanian age and the mud- stones around the above localities are referable to Member My3. Incidentally, as a result of Y. Inoue’s examination of foraminifera, the strata exposed in the source area of the Sanjussen-zawa, including localities R7238, R7231, R7232, R7233 and R7234, have proved to be Member My5 (middle to upper part of the Cenomanian) (for details see Nishida et al., 1998a). The two members My3 and My5 are probably in fault contact (Figure 1). Repository The specimens described below have numbers with the prefix TKD, which is the abbreviation of “Tokyo Kyoiku Daigaku [Tokyo University of Education|”, where A.l. was a student. Since this university was closed, As collection of ammonoids from the Soeushinai area under TKD numbers has been temporarily stored in the Department of Geology, Mesoturrilites from Hokkaido 37 i # My3 ara AI-72803 i VER) re ’ FH 45° S - 100m S| Figure 1. Route map along the upper course of the Sanjussen-zawa, cited from Nishida et al., 1998a by permission. Inset is a map of Hokkaido in which the Soeushinai area is indicated by an arrow. Small solid circle : megafossil (in situ), cross : ditto (trantported nodule), solid square : microfossil sample, empty square: rock sample, tiny empty circle: conglomerate, dots: sandstone, grass: no outcrop, blank along the route: mudstone, broken line: fault (inferred), chain : boundary of lithostratigraphic units (members). All the locality numbers should have prefix R, except for Al-72803. Kyushu University in Fukuoka, but they should be eventually returned to the Deparrtment of Geosciences, Tsukuba University, Tsukuba, 305-0006 Japan, which is the new guise of the TKD. Morphological terms For the morphological terms used to describe the turrilitid ammonoids, we follow those of Wright and Kennedy (1996). Setting the apex of the turrical shell at the top, the terms upper and lower or adapical and adapertural | =adoral| are defined and the rows of tubercles or ribs on the face of each whorl are described in descending order as the first, the second and so on. Palaeontological description Order Ammonoidea Zittel, 1884 Suborder Ancyloceratina, Wiedmann, 1966 Family Turrilitidae Gill, 1871 Genus Mesoturrilites Breistroffer, 1953 Type species.—Turrilites aumalensis Coquand (1862, p. 323, pl. 35, fig. 5), by original designation of Breistroffer (1953, p. 1351). Diagnosis.— Turrilitid ammonoid with four rows of tubercles or ribs ; the upper row made up of ribs or rounded tubercles, the second and the third rows spirally elongated tubercles on semicontinuous, narrow ridges separated by a groove ; the fourth row of weak tubercles at the outer edge of the lower whorl surface ; faint ribs may be elongated from the fourth row of tubercles toward a narrow umbilicus. Remarks.—The lectotype and paralectotypes of the type species have been photographically illustrated by Wright and Kennedy (1996, text-fig. 146A-G). At present five species are known in Mesoturrilites. The distinction between species is based on the size of the apical angle, mode of ribbing and/or tuberculation, whorl shape etc. Atabekian (1985, p.75) referred Turrilites col- canapi Boule, Lemoine and Thevenin, 1907 to Mesoturrilites. However, we agree with Spath (1937, p. 523) and also Wright and Kennedy (1996, p. 323) on their assignment of T. col- canapi to Ostlingoceras. The phylogenetic origin of Mesoturrilites is uncertain, but it can likely be sought in some form of Mariella. A sulcate variety of Mariella oehlerti (Pervinquiere) may be a candidate, as Pervinquiére (1910, p.55, pl.5, fig.17) has already mentioned its affinity to Mesoturrilites aumalensis. Wright and Kennedy (1996, p. 346) have suggested Mariella bicar- inata (Kner) as another allied form. The type species and some other species of Mesoturrilites have been recorded from the Lower Cenomanian of both ine 38 Tatsuro Matsumoto and Akitoshi Inoma Tethys and Boreal provinces. Mesoturrilites boerssumensis (Schlüter, 1876) Figures 2 and 3 Turrilites börssumensis Schlüter, 1876, p. 129, pl. 38, figs, 6, 7. Turrilites (Mesoturrilites) boerssumensis Schlüter. Immel, 1979, p. 636, pl. 4, fig. 4; Hiss, 1982, p. 190, pl. 7, figs. 11, 12 ; Atabekian, 1985, p. 75, pl. 27, figs. 3, 4. Mesoturrilites boerssumensis (Schlüter). Wright and Ken- Figure 2. Mesoturrilites boerssumensis (Schlüter). 1. TKD30089A, two lateral (a,b) and basal (c) views. 2. TKD30089B, two lateral (a, b) views. 3. TKD30089C, two lateral (a, b) views. All x 2. Figure 3. Mesoturrilites boerssumensis (Schlüter). Suture of TKD30089C, showing relative position of the ribs and tubercles by dotted lines. Approximately x 8. nedy, 1996, p. 347, pl. 105, figs. 4, 20 (with full synonymy) ; Lehmann, 1998, p. 36, pl. 5, fig. 5. Lectotype.—The original of Schlüter, 1876, pl. 38, figs. 6, 7, from the Cenomanian Planer near Borssum, Germany, by subsequent designation of Juignet and Kennedy (1976, p. 67). Material—Four specimens, TKD30089A (Figure 2-1), TKD30089B (Figure 2-2), TKD30089C (Figure 2-3 ; Figure 3) and TKD30089D (unillustrated). They were removed by Al. from a transported nodule at locality Al-72803 in the upper reaches of the Sanjussen-zawa of the Soeushinai area, northwestern Hokkaido (Figure 1). Description.—TKD30089A consists of four whorls with estimated tower height 28.8 mm, apical angle about 19°, height and diameter of the preserved last whorl 5.4 mm and 11.2mm respectively. Other three are smaller than the above and incomplete, representing younger stages. The main part of the exposed whorl face is flattened or slightly convex and the interwhorl junction is feebly im- pressed. The ornament is typical for Mesoturrilites. On the upper half of the exposed whorl face there are slightly prorsiradiate ribs of moderate breadth and density (Figure 2- 1). They number 21 per whorl at diameter of 11mm in TKD30089A and 16 or 15 at diameter 7 or 6mm in TKD30089B or TKD30089C. At about the middle of the whorl face the ribs terminate at tubercles of the first row. These tubercles are subrounded at the base and pointed at the top, as far as the test is well preserved. The tubercles of the second row are narrowly clavate and rest on a blunt spiral ridge. They correspond in number to the tubercles of the first row but are displaced adaperturally. The space between the first and the second rows of tubercles forms a smooth band and may appear to be slightly concave on the internal mould. The tubercles of the third row are narrowly clavate and aligned along the narrow ridge along the lower seam of the whorl. The narrow interspace between the second and the third rows of clavi is distinctly sulcate. As is shown by TKD30089A, the spiral groove between the second and third rows of semi-continuous ridges is immedi- ately above the interwhorl junction in early growth stages, but later it is covered by the shell layer of the succeeding whorl (Figure 2-1). The tubercles of the fourth row are close to those of the third row, but they are aligned on the outer margin of the lower whorl face. Weak ribs run from them toward a narrow umbilicus, showing slightly rursiradiate Curvature (Figure 2-1c). A septal suture of a young stage is exposed on the whorl face of TKD30089C. As is shown in Figure 3, the saddle E/L is much broader than L/U. The relative disposition of the tubercles with respect to the sutural elements in shown is the same figure. Discussion.—The specimens described above are un- doubtedly identified with Mesoturrilites boerssumensis (Schluter, 1876), redefined by Wright and Kennedy (1996, p. 347). In view of the variation of the rib density with growth and between individuals, the 17 ribs to a whorl specified in Schlüter's (1876, p. 636) description may not be incorrect. Hiss (1982, p.190) counted 20 ribs on an example from Westphalia. Wright and Kennedy (1996, p. 347) estimated Mesoturrilites from Hokkaido 39 as many as 24-26 ribs per whorl in a specimen from England, but 9 or 10 ribs are shown on its illustrated face of slightly less than half a whorl (op. cit., pl. 105, fig. 4) as in our TKD30089A (Figure 2-1). Hitherto described specimens, comprising those from Hokkaido, are more or less small, with diameters of the preserved last whorl less than 25mm. The small size may be, therefore, a diagnostic character of this species. How- ever, further investigation is required to search out a com- pletely preserved specimen with a rostrate peristome and also to examine the problem of dimorphism. Occurrence.—As for material. M. boerssumensis has been reported from the Lower Cenomanian of Germany (Westphalia and Bavaria), England, Poland and southern Turkmenistan (see synonymy list). Now its distribution is extended to Hokkaido. This may be the first record of Mesoturrilites from the northern Pacific region. Acknowledgements We are much indebted to C.W. Wright and W.J. Kennedy for their kind help during this study. Thanks are extended to Tamio Nishida, Seiichi Toshimitsu and Kazuko Mori for practical support. References cited Atabekian, A.A., 1985: Turrilitids of the late Albian and Cenomanian of the southern part of the USSR. Acad- emy of Sciences of the USSR, Ministry of Geology of the USSR. Interdepartmental Stratigraphic Committee of the USSR, Transactions, vol. 14, p. 1-112, pls. 1-34. (in Russian) Boule, M., Lemoine, P. and Thevenin, A., 1907 : Cepha- lopode crétacés des environs de Diego-Suarez. An- nales de Paléontologie, vol. 2, p. 1-56, pls. 1-8. Breistroffer, M., 1953: L’evolution des Turrilitides albiens et cenomaniens. Comptes Rendus Hebdomadaires des Sciences de l'Académie des Sciences, vol. 237, p. 1349-1351. Coquand, H., 1862: Géologie et paléontologie de la region sud de la Province de Constantine. Mémoires de la Société d’Emulation de la Provence, Marseille, vol. 2, p. 1-320, 321-341 (supplement), pls. 1-35. Hashimoto, W., Nagao, S. and Kanno, S., 1965 Soeushinai. Explanatory Text of the Geological Map of Japan, scale 1: 50,000, p.1-92, quadrangle map. Geological Sur- vey of Hokkaido. (in Japanese with English abstract) Hiss, M., 1982 : Ammoniten des Cenomans von Südrand der westfälischen Kreide zwischen Unna und Möhnesee. Paläontologische Zeitschrift, vol. 56, p. 177-208, pls. 7- 9. Immel, H., 1979: Cenoman-Ammoniten aus den Losen- steiner Schichten der Bayerischen-Alpen. In, Wied- mann, |. ed., Aspekte der Kreide Europas. International Union of Geological Sciences, Ser. A, vol. 6, p. 607-644, 4 pls. Inoma, A., 1980: Mid-Cretaceous ammonites from the Shumarinai-Soeushinai area, Hokkaido. Part2. Pro- fessor Saburo Kanno Memorial Volume, Tsukuba, p. 167-183, pls. 21-22. Juignet, P. and Kennedy, W.J., 1976: Faunes d’ammonites et biostratigraphie comparee du Cenomanien du nord ouest de la France (Normandie) et du sud de l’Angleter- re. Bulletin trimestriel, Société Geologique Normandie Amis Muséum Havre, vol. 63, p. 1-193, pls. 1-34. Lehmann, J., 1998: Systematic palaeontology of the ammo- nites of the Cenomanian-Lower Turonian (Upper Cretaceous) of northern Westphalia, north Germany. Tubingen Geowissenschaftliche Arbeiten (TGA), Reihe A, vol. 37, p. 1-58, pls. 1-5. Matsumoto, T. and Inoma, A., 1975 : Mid-Cretaceous ammo- nites from the Shumarinai-Soeushinai area, Hokkaido. Part |. Memoirs of the Faculty of Science, Kyushu University, Series D, Geology, vol. 23, no. 2, p. 263-293, pls. 38-42. Matsumoto, T. and Inoma, A., 1991: The mid-Cretaceous ammonites of the family Kossmaticeratidae from Japan. Part 3. Descriptions of the species from the Shuma- rinai-Soeushinai area of Hokkaido. Palaeontological Society of Japan, Special Papers, no. 33, p. 103-122, pls. 25-30. Nishida, T., Matsumoto, T. and Inoue, Y., 1998a: For- aminifera from the Cretaceous System in the Shuma- rinai Valley of Hokkaido. Journal of the Faculoy of Culture and Education, Saga University, vol. 3, no.1, p. 301-331. (in Japanese with English abstract) Nishida, T., Matsumoto, T., Kawashita, Y., Egashira, N., Aizawa, J. and Ikuji, Y., 1997: Biostratigraphy of the middle part of the Cretaceous Yezo Group in the Soeushinai area of Hokkaido—with special reference to the transitional part from Lower to Upper Cretaceous : supplement—. Journal of the Faculty of Culture and Education, Saga University, vol.1, no.1, p. 237-279. (in Japanese with English abstract) Nishida, T., Matsumoto, T., Kawashita, Y., Egashira, N. and Aizawa, J., 1998b: Characteristics of the Cretaceous stratigraphy in the Shumarinai Valley of Hokkaido. Journal of the Faculty of Culture and Education, Saga University, vol.1, no. 2, p. 143-181. (in Japanese with English abstract) Nishida, T., Matsumoto, T., Yokoi, K., Kawashita, Y., Kyuma, Y., Egashira, N., Aizawa, J., Maiya, S., Ikuji, Y. and Yao, A., 1996: Biostratigraphy of the Cretaceous Middle Yezo Group in the Soeushinai area of Hokkaido—with special reference to the transitional part from Lower to Upper Cretaceous—. Journal of the Faculty of Educa- tion, Saga University, vol.44, no.1, p.65-149. (in Japanese with English abstract) Pervinquière, L., 1910: Sur quelques ammonites du Crétacé algérien. Mémoires de la Société Geologique de France, Paléontologie 17, memoir 42, p. 1-86, pls. 1-7. Schlüter, C., 1876: Cephalopoden der oberen deutschen Kreide. Palaeontographica, vol. 24, p. 121-264, pls. 36- 55. Spath, L.F., 1937 : A monograph of the Ammonoidea of the Gault, part 12. Monograph of the Palaeontographical Society, London, p. 49-540, pls. 57-58. Wright, C.W. and Kennedy, W.J. 1996 : The Ammonoidea of the Lower Chalk, part 5. Monograph of the Palaeonto- graphical Society, London, no. 601, p. 320-403, pls. 95 124. 40 Tatsuro Matsumoto and Akitoshi Inoma Hokkaido 4b#i8, Sanjussen-zawa =-+-# Ri, Shumarinai K##N, Soeushinai EN, Uryu N, Yezo thas Paleontological Research, vol. 3, no. 1, pp. 41-48, 5 Figs., April 30, 1999 © by the Palaeontological Society of Japan Early Silurian actinocerid and orthocerid cephalopods from the Kerman area, East-Central Iran SHUJI NIKO’, YOSHITAKA KAKUWA’, DAISUKE WATANABE’ and RYO MATSUMOTO’ ‘Department of Environmental Studies, Faculty of Integrated Arts and Sciences, Hiroshima University, Higashihiroshima 739-8521, Japan "Department of Earth Science and Astronomy, College of Arts and Sciences, University of Tokyo, Komaba 153-0041, Japan “Geological Institute, University of Tokyo, Hongo 113-0033, Japan Received 23 September 1998 ; Revised manuscript accepted 22 February 1999 Abstract. Six species of uncoiled cephalopod, including the actinocerids Actinoceratidae, gen. and sp. indet., Armenoceras banestanense sp. nov., A. sp., Elrodoceras sp. and Huroniella iranica sp. nov., and an orthocerid Proteoceratidae ?, gen. and sp. indet., are present in collections made recently from an unnamed formation near Banestan village in the Kerman area of southern East-Central Iran. The cephalopod fauna contains forms closely related with those from Laurentia, and is considered to be of Early Silurian age. This discovery reveals that the geologic age of these cephalopod-bearing horizons should be revised from a vague late Ordovician or early Silurian one. These horizons are correlative with the Niur Formation in the Shirgesht area of northern East-Central Iran. Key words: Actinocerida, cephalopods, Early Silurian, Iran, Orthocerida Introduction and geologic setting During the course of field work in February, 1996, several uncoiled cephalopods were discovered by two of us (Y.K. and D.W.) at three localities near Banestan village in the Kerman area of southern East-Central Iran (Figure 1). The purpose of this paper is to document the fauna and to discuss its implications. The specimens are deposited in the University Museum of the University of Tokyo (UMUT). Until its separation and northward drifting at or near the Permian-Triassic boundary, the Iran terrane belonged to the Gondwana continent, and the Kerman area was part of a carbonate platform around the margin of Gondwana (e.g., Lensch et al., 1984). The geology of the Kerman area has been described by Huckriede et al. (1962), Zohrenbakhsh and Vahdati Daneshmand (1992) and Richards et al. (1994). These investigatiors discerned three units in the Lower to Middle Paleozoic strata: Upper Cambrian to Lower Or- dovician carbonates of the Mila Formation, the Arenig (upper Lower Ordovician) graptolite shale of the Katkoyeh Forma- tion, and an unnamed formation probably ranging from Upper Ordovician to Middle Devonian that mainly consists of clastics with subordinate carbonates. The cephalopods described herein occur in argillaceous and/or bioclastic limestone of the unnamed formation (Figure 2). The cephalopod-bearing horizons have been described as “orthoceras limestone” by Huckriede et al. (1962), and regard- ed as being of late Ordovician or early Silurian age. How- ever, the exact biostratigraphic range of the cephalopod- bearing horizons has so far been a matter of debate. Detailed analysis of morphologic features of the present cephalopods resulted in the identification of five Early Silurian actinocerid and one orthocerid species that provide insights into the precise age and paleobiogeographic affin- ities of the fauna. This is the first modern taxonomic treat- ment of Silurian cephalopods from the Iran terrane. Systematic paleontology Subclass Actinoceratoidea Teichert, 1933 Order Actinocerida Teichert, 1933 Family Actinoceratidae Saemann, 1853 Genus and species indeterminate Figures 3-7, 5-5, 6 Discussion.—A single incomplete specimen of a gently cyrtoconic (?) phragmocone is assigned to the Actinocer- atidae, genus and species indeterminate, based on its rela- tively long and normal cyrtochoanitic septal necks and the high ratio (at least 3.2) of maximum diameter/length of its siphuncular segments. The restricted development of the annulosiphonate 42 Shuji Niko et al. = N \ \ \ 2 ~ by) © ise) Figure 1. Index map of fossil localities (1-3) in the Ker- man area (Small arrow in inset), southern East-Central Iran. deposits on the ventral siphuncular wall and the straight radial canals projecting to the vicinity of brims are an unusual diagnosis for the family and indicate a possibility that the species represents a new genus. Unfortunately the ventral shell is not preserved in the only specimen available. Until additional material is found, the present material is consid- ered too poor to justify naming it to the generic level. Material and occurrence.—UMUT PM 27332, 72 mm in length, from locality 3. Family Armenoceratidae Troedsson, 1926 Genus Armenoceras Foerste, 1924a Type species.—Actinoceras hearsti Parks, 1913. shale & siltstone [= © Do Oosr0 = conglomerate E Di 5 == = limestone T ® E 2 dolostone € 3 pillow lava & volcanic breccia Inne ale | LI Tun | [hi] Katkoyeh Formation If | ; el is à 0 [0] al D le Al . oll: | 200m (part) Oo Formation Mila Figure 2. Generalized stratigraphic section of the Lower to Middle Paleozoic rocks near Banestan village in the Ker- man area. Stratigraphic horizons of each locality are indicat- ed. Armenoceras banestanense sp. nov. Figures 3-1—6 Diagnosis.— Armenoceras with smaller ratio of maximum siphuncular diameter to shell diameter (approximately 0.3- 0.4), very narrow adnation areas in dorsal siphuncular wall ; cameral deposits well developed ; central canal situated on dorsal margin. Description.—Orthoconic shells with circular cross sec- tions, moderate shell expansion for the genus, lacking Figure 3. 1-6. Armenoceras banestanense sp. nov., 1-4,6: holotype, UMUT PM 27328, 1, dorsoventral thin section, venter on left, x2, 2, dorsoventral thin section, showing details of ventral wall of siphuncle, 14, 3, dorsoventral thin section, showing details of dorsal wall of siphuncle, note very narrow adnation area, 14, 4, dorsoventral thin section, showing details of ventral shell, x5, 6, transverse thin section of adoral end, venter down, x2, 5: paratype, UMUT PM 27327, weathered surface of dorsal side, coated with ammonium chloride, x2. 7. Actinoceratidae, gen. and sp. indet., UMUT PM 27332, dorsoventral thin section, venter on right, x 2. Early Silurian cephalopods from Iran 44 conspicuous surface ornamentation ; adoral end of imper- fect phragmocone of holotype attains approximately 25 mm (slightly deformed) in diameter. Septa closely spaced, moderately shallow; siphuncle large, ratio of maximum siphuncular diameter to shell diameter is small for genus, approximately 0.3-0.4, submarginal in position ; septal necks very short, 0.15-0.21 mm in length, strongly recurved cyrto- choanitic ; brims short for genus, 0.44 mm in well preserved dorsal brim of holotype, in contact with apical surface of septa; diameter of septal foramen 5.9-8.9 mm in holotype ; connecting rings broadly expanded ; adnation areas moder- ate to relatively narrow (their length in dorsoventral section approximately 0.9 mm) in ventral siphuncular wall, and very narrow (do. approximately 0.3 mm) in dorsal siphuncular wall ; maximum diameter/length ratio of siphuncular segments 3.5-4.0. Cameral deposits well developed, episeptal-mural and forming circumsiphuncular ridges, additional hyposeptal deposits recognized in ventral side of camerae; ventral endosiphuncular deposits fusing to form thick lining on siphuncular wall, differentiated into outer annuli and inner lining deposits ; profile of outer annuli laterally elongated elliptical in longitudinal section; development of endosi- phuncular deposits on dorsal siphuncular wall weak, sepa- rated annuli with semicircular profile in longitudinal section. Central canal situated on dorsal margin, branching off narrow radial canals, of which distal parts are curved adorally ; perispatia small, situated near adoral end of each connecting ring. Discussion.—Armenoceras banestanense sp. nov. is most similar to A. hearsti (Parks, 1913 ; 1915, pl. 6, fig. 5; Foerste, 1924a, pl. 13, fig. 4) which has a siphuncular position and a form ratio of the siphuncular segments like the new species. Armenoceras hearsti was reported from “Limestone Rapids” on the Severn River, Ontario, Canada, and derived from the Ekwan River or Attawapiskat Formation of late Llandovery (Early Silurian) age (Jin et al., 1993). However the former is distinguishable from the latter by its smaller siphuncle (ratio of maximum siphuncular diameter to shell diameter approxi- mately 0.45 in A. hearsti versus 0.3-0.4 in A. banestanense), its somewhat weaker inflation of the connecting rings with the narrower adnation area, and the marginal position of its central canal. The brims of Armenoceras banestanense and the cooc- curring A. sp. (this report) are frequently missing or obscured by diagenesis, thus they are apt to be incorrectly described as “achoanitic”. Material and occurrence.—Holotype, UMUT PM 27328, an incomplete phragmocone, 51 mm in length ; paratype, UMUT PM 27327, an incomplete phragmocone, 42 mm in length. Both from locality 3. Etymology.—The specific name is derived from the village Shuji Niko et al. named Banestan near the type locality. Armenoceras sp. Figures 4-5,7,8 Description.—Orthoconic shells with gradual shell expan- sion, shell diameter reaches 20 mm at adoral end of largest specimen (UMUT PM 27329). Siphuncle subcentral in position, consisting of strongly recurved cyrtochoanitic septal necks and expanded connecting rings with relatively wide adnation area; brims in contact with septa; maximum diameter/length ratio of siphuncular segments approximately 2.5. Cameral deposits episeptal-mural and hyposeptal ; endosiphuncular deposits of annuli have elliptical profile in longitudinal section. Nearly straight radial canals connect with prespatia in apical shell. Discussion.—This species is easily distinguished from Armenoceras banestanense sp. nov. by its subcentral siphun- cular position and the smaller form ratio of the siphuncular segments. Material and occurrence.—Two incomplete phragmocones, UMUT PM 27329, 62 mm in length, and 27330, 61 mm in length, from locality 3. Genus Elrodoceras Foerste, 1924b Type species.—Cyrtoceras indianense Miller, 1892. Elrodoceras sp. Figures 5-1—3 Description.—Siphuncle gently curved (?) and large, attains at least 15.5 mm in maximum diameter, with relatively low ratio of maximum diameter/length in siphuncular segment for armenoceratids, at approximately 2.5-2.7 ; siphuncular posi- tion submarginal (?). Septal necks bend adapically, thus septal foramen is funnel-shaped ; brims strongly recurved cyrtochoanitic, in contact with septa; connecting rings form very wide adnation area and moderately inflated free parts. Cameral deposits episeptal-mural and hyposeptal ; endosi- phuncular deposits well developed, annulosiphonate. Cen- tral canal surrounded by lining deposits that are darker in color than annulosiphonate deposits ; radial canal arched with branches. Discussion.—Except for the deposit-filled siphuncle, the shell of this only known specimen is broken and weathered on the dorsum, thus accurate shell shape and siphuncular position can not be determined in the present material. Nevertheless, this species appears most similar to Elrodocer- as in its siphuncular morphology such as the funnel-shaped Figure 4. venter on left, of ventral wall of siphuncle, 1-4, 6. Huroniella iranica sp. nov., holotype, UMUT PM 27326, isolated siphuncle, 1, dorsoventral thin section, <2, 2, transverse thin section of apical end, venter down, <2, 3, dorsoventral thin section, showing details <5, 4, dorsoventral thin section, showing details of dorsal wall of siphuncle, <5, 6, dor- soventral thin section, showing details of septal neck and radial canal in ventral wall of siphuncle, note contact layer and depression on apical surface of septum, section, venter on right, <14. 5,7,8. Armenoceras sp., 5,7: UMUT PM 27330, 5, dorsoventral thin <2, 7, dorsoventral thin section, showing details of ventral wall of siphuncle, x14, 8: UMUT PM 27329, weathered surface of ventral side, coated with ammonium chloride, x 2. Early Silurian cephalopods from Iran 46 Shuji Niko et al. septal foramen, arched radial canals and relatively low form ratio of the siphuncular segments. Material and occurrence.—UMUT PM 27331, 55 mm in length, from locality 3. Family Huroniidae Foerste and Teichert, 1930 Genus Huroniella Foerste, 1924a Type species.—Huronia inflecta Parks, 1915. Huroniella iranica sp. nov. Figures 4-1—4, 6 Diagnosis.—Huroniella with asymmetrical connecting rings ; siphuncular segments short ; adoral bending of septa lacking; width of septal foramen/distance of neighboring septal necks 2.3-3.0; perispatia wide, attain distal end of brim. Description.—Large straight siphuncle, 20.5 mm in lateral diameter of apical end of holotype; septal necks short, approximately 0.5mm in length, strongly recurved cyrto- choanitic ; brims 0.63-0.68 mm in length, in contact with apical surface of septa; diameter of septal foramen 12.5-14. O mm; shape of connecting rings asymmetrical in dor- soventral section, ventral connecting rings strongly inflated, bluntly pointed arcs with obliquely adoral direction in longitu- dinal section ; adnation area in adoral surface of septa very wide, forming contact layer by thickening of connecting ring ; in contrast to adoral surface of septa, relatively narrow in apical surface, contact layer also recognized where septa are weakly depressed ; dorsal connecting rings semicircular with narrow adnation area lacking evident contact layer ; siphuncular segments short for huroniids, width of septal foramen/distance of neighboring septal necks 2.3-3.0. Endosiphuncular deposits of annuli well developed leaving large central canal in a position slightly shifted from axis ; radial canals curving adapically and branching, to join wide perispatia, which attain distal end of brim. Discussion.—Huroniella iranica sp. nov. appears to be most like H. persiphonata (Billings, 1857 ; Foerste, 1927, pl. 44, fig. 1; Teichert, 1933, figs. 4, 20) from the upper Llandovery Jupiter Formation of Anticosti Island, Canada. The Lau- rentian species shares the asymmetrical profile of its con- necting rings with the present new species. The most obvious difference between these species is the septal morphology, i.e., a strong adoral bending of the septum is recognized in Huroniella persiphonata, but only a weak depression on the adoral septal surface is representative of H. iranica. In addition, the width of septal foramen/ distance of neighboring septal necks ratio (approximately 2 in H. persiphonata versus 2.3-3.0 in H. iranica) is also a diagnostic feature. Huroniella inflecta (Parks, 1915, pl. 6, fig. 4 ; Foerste, 1924a, pl. 16, figs. 2a, b; Teichert, 1933, fig.12), known from the “Limestone Rapids” in Ontario, is distinguished from the present species by having more strongly inflated dorsal connecting rings with a nearly symmetrical profile in dor- soventral section. Material and occurrence.—Holotype, UMUT PM 27326, an isolated and incomplete siphuncle 65 mm in length, from locality 1. Etymology.—The specific name in derived from Iran. Subclass Nautiloidea Agassiz, 1847 Order Orthocerida Kuhn, 1940 Superfamily Pseudorthocerataceae Flower and Caster, 1935 ? Family Proteoceratidae Flower, 1962 Genus and species indeterminate Figures 5-4, 7 Discussion.—The poorly preserved specimen consists of a gradually expanding orthoconic shell with relatively short camerae, subcentral siphuncle consisting of short cyrto- choanitic septal necks and inflated connecting rings. Its maximum diameter/length ratio of siphuncular segments is approximately 1.5, and cameral deposits are episeptal. This species probably belongs to the Proteoceratidae, and its large siphuncular segment ratio for an orthocerid suggests a possible relationship with Ephippiorthoceras, although the material is insufficiently preserved to identify any further. Material and occurrence.—Single incomplete phrag- mocone, UMUT PM 27333, 74 mm in length, from locality 2. Stratigraphic and paleobiogeographic implications The cephalopod species recognized at each locality are as follows : locality 1, Huroniella iranica sp. nov.; locality 2, Proteoceratidae ?, gen. and sp. indet.; and locality 3, Actinoceratidae, gen. and sp. indet., Armenoceras banes- tanense sp. nov., A. sp. and Elrodoceras sp. The most useful taxon for correlation is Huroniella, whose range is known with certainty from late Llandovery to early Wenlock strata in Laurentia and Baltica. Species similar to Huroniella iranica are found in the Anticosti Island and Hudson Bay areas and are of late Llandovery age. Flrodoceras is the only Silurian cephalopod previously known from Laurentia, Avalonia, Baltica and Siberia. Armenoceras banestanense sp. nov. is related to the late Llandovery species A. hearsti from the Hudson Bay area, and the genus is cosmopolitan Figure 5. 1-3. Elrodoceras sp., UMUT PM 27331, 1, dorsoventral thin section, venter on right, x2, 2, dorsoventral thin section, showing details of ventral wall of siphuncle, 5, 3, dorsoventral thin section, showing details of septal necks, radial canal and connecting ring in ventral wall of siphuncle, note adapical bending of septal necks, «14. 4, 7. Proteoceratidae ?, gen. and sp. indet., UMUT PM 27333, 4, longitudinal thin section, x2, 7, longitudinal thin section, showing details of siphuncle, <8. 5,6. Actinoceratidae, gen. and sp. indet., UMUT PM 27332, 5, dorsoventral thin section, showing details of ventral wall of siphuncle, arrows indicate septal necks, of siphuncle, 14. <14, 6, dorsoventral thin section, showing details of dorsal wall 47 Early Silurian cephalopods from Iran 48 Shuji Niko et al. and ranges from Middle Ordovician to Late Silurian in age. Besides cephalopods, the Wenlockian bryozoan species Trematopora beikhemensis is identified by S. Sakagami (per- sonal communication) from locality 1. Although locality 2 lacks a clear age indicator, lithologically the three horizons may belong to a stratigraphic unit without notable breaks. On the basis of this evidence, we infer that at least the cephalopod-bearing horizons in the unnamed formation indicate a late Llandovery (or early Wenlock) age, and are lithologically and chronostratigraphically correlative with the Niur Formation (Ruttner et al., 1968) in the Shirgesht area of northern East-Central Iran. On the other hand, the affinity of the cephalopod fauna is apparently with northeastern Laurentia. This new material suggests a faunal connection between Gondwana and Laurentia during Early Silurian times. Acknowledgments We with to thank Sumio Sakagami for providing unpub- lished data on a bryozoan associated with the present cephalopods. This research was supported by grant 0704194 from the Japanese Ministry of Education. References Billings, E., 1857: Report for the year 1856, of E. Billings Esq., palaeontologist, addressed to Sir William E. Logan, provincial geologist. Geological Survey of Canada. Report of Progress, for the years 1853-54-55-56, p. 247-345. Flower, R.H., 1962 : Notes on the Michelinoceratida. New Mexico Bureau of Mines and Mineral Resources, Mem- oir 10, p. 21-42, pls. 1-6. Flower, R.H. and Caster, K.E., 1985: The stratigraphy and paleontology of northwestern Pennsylvania. Part Il: Paleontology. Section A: The cephalopod fauna of the Conewango Series of the Upper Devonian in New York and Pennsylvania. Bulletins of American Paleontology, vol. 22, p. 199-271. Foerste, A.F., 1924a: Silurian cephalopods of northern Michigan. Contributions from the Museum of Geology, University of Michigan, vol. 2, p. 19-86, pls. 1-17. Foerste, A.F., 1924b: Notes on American Paleozoic cephalopods. Denison University Bulletin, Journal of the Scientific Laboratories, vol. 20, p. 193-268, pls. 21 42. Foerste, A.F., 1927 : Cephalopoda. In, Twenhofel, W.H. ed, Geology of Anticosti Island, p. 257-321, pls. 27-58. Canada Geological Survey, Memoir 154. Foerste, A.F. and Teichert, C., 1930: The actinoceroids of “ East-Central North America. Denison University Bulle- tin, Journal of the Scientific Laboratories, vol. 25, p. 201- 296, pls. 27-59. Huckriede, R., Kürsten, M. and Venzlaff, H., 1962. Zur Geologie des Gebietes zwischen Kerman und Sagand (Iran). Beihefte zum Geologischen Jahrbuch, no. 51, p. 1-197. Jin, J., Caldwell, W.G.E. and Norford, B.S., 1993: Early Silurian brachiopods and biostratigraphy of the Hudson Bay Lowlands, Manitoba, Ontario, and Quebec. Geo- logical Survey of Canada, Bulletin, vol. 457, p. 1-221. Lensch, G., Schmidt, K. and Davoudzadeh, M., 1984 : Intro- duction to the geology of Iran. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen, vol. 168, p. 155-164. Miller, S.A., 1892 : Palaeontology. Annual report of Depart- ment of Geology and Natural Resources, Indiana, vol. 17, p. 611-705, pls. 1-20. Parks, W.A., 1913: Notes on fossils. In, Tyrrell, J.B., Hudson Bay Exploring Expedition, 1912. Twenty-second Annual Report of the Ontario Bureau of Mines, part 1, p. 161-209. Parks, W.A., 1915: Palaeozoic fossils from a region south- west of Hudson Bay. Transactions of the Royal Canadian Institute, vol. 11, p. 1-95, pls. 1-7. Rickards, R.B., Hamedi, M.A. and Wright, A.J., 1994: A new Arenig (Ordovician) graptolite fauna from the Kerman district, East-Central Iran. Geological Magazine, vol. 131, p. 35-42. Ruttner, A., Nabavi, M.H. and Hajian, J., 1968: Geology of the Shirgesht area (Tabas area, East Iran). Geological Survey of Iran, Report 4, p. 1-133. Saemann, L., 1853: Ueber die Nautiliden. Palaeontogra- phica, vol. 3, p. 121-167, pls. 18-21. Teichert, C., 1933: Der Bau der actinoceroiden Cephalopoden. Palaeontographica, Abteilung A, vol. 78, p. 111-230, pls. 8-15. Troedsson, G.T., 1926 : On the Middle and Upper Ordovician faunas of northern Greenland, 1. Cephalopods. Med- delelser om Gronland, vol. 71, p. 1-157, pls. 1-65. Zohrehbakhsh, A. and Vahdati Daneshmand, F., 1992: Geological Quadrangle Map of Iran 1: 250.000, sheet Rafsanjan. Geological Survey of Iran, Tehran. Paleontological Research, vol. 3, no. 1, pp.49-56, 3 Figs., April 30, 1999 © by the Palaeontological Society of Japan Occurrence of Carboniferous corals from the Geumcheon Formation of Danyang area, Korea JEONG- YUL KIM’, HYO-NYONG LEE’ and CHANG- HI CHEONG’ ‘Department of Earth Science Education, Korea National University of Education, Cheongwon, Chungbuk 363-791, Korea "Department of Geological Sciences, Seoul National University, Seoul 151-749, Korea Received 2 October 1998 ; Revised manuscript accepted 5 February 1999 Abstract. Two species of Carboniferous coral, Arachnastraea manchurica and Diphyphyllum delicatum, are described for the first time from the upper part of the Geumcheon Formation of the Danyang area, Korea. They were previously reported as Devonian corals, Disphyllum sp. and Phillipsastraea sp. Associated fossils are fusulinids, including Beedeina schellwieni, B. siviniensis, B. samarica, B. sp., Fusulina cylindrica, F. sp., Fusulinella mosquensis, Fusulinella provecta, Neostaffella sphaeroidea, and Ozawainella turgida. Occurrence of these corals and fusulinids suggests that the upper part of the Geumcheon Formation is middle Moscovian in age. Key words: Carboniferous, coral, Danyang area, Korea Introduction Yabe and Suzuki (1955) first reported specimens of corals from a limestone bed in Danyang area, Korea. They as- signed them in open nomenclature to colonial corals of Devonian type as Disphyllum sp. and Phillipsastraea sp. and suggested that Devonian deposits existed in Danyang area. Unfortunately, their specimens were lost. Furthermore, they figured only one weathered surface and one polished-slab figure of Disphyllum sp. and offered no systematic descrip- tions. On the basis of a second discovery of coral specimens of Phacellophyllum sp.? (Disphyllum sp.) associated with fusulinids including Fusulina sp., Fusulinella sp., and Neostaf- fella sp. from nearly the same horizon as that of Yabe and Suzuki (1955), Cheong (1972) saw a problem in the Danyang area, with a Devonian dating. He mentioned that the lime- stone containing the coral is not Devonian but Moscovian (Late Carboniferous) in age and surmised that this coral, which had been known as a Devonian type, probably sur- vived into the Carboniferous. Several months after Cheong’s report, Kato (1972) reex- amined the figures of Yabe and Suzuki (1955) and briefly documented that Disphyllum sp. and Phillipsastraea sp. re- ported from the Danyang area by Yabe and Suzuki (1955) are Diphyphyllum sp. and Arachnastraea sp. respectively. Recently well preserved coral specimens, which are close- ly associated with abundant fusulinids, were discovered from a limestone bed of the Geumcheon Formation by the present authors. The purpose of this paper is to report an additional occurrence of Carboniferous coral specimens, which are described here as Diphyphyllum delicatum and Arachnastraea manchurica, and to compare these with the Devonian corals Disphyllum sp. and Phillipsastraea sp. illustrated by Yabe and Suzuki (1955). Geologic setting and fossil locality General geological studies in the Danyang area have previously been carried out by many investigators (Kobatake, 1942 ; Brill, 1957; Lee and Kim, 1966; Son et al, 1967; Park and Cheong, 1975 ; Park et al., 1975; Kim, 1981). Kim (1971) studied the Paleozoic and Mesozoic paleocurrents of the Danyang Coalfield on the basis of sedimentary struc- tures. Structural analysis and tectonic studies of the Danyang area have been recently carried out by Cho et dl. (1986), Kim and Koh (1992), Kim et al. (1992a), Kim et al. (1992b), and Kim et al. (1994). The Permo-Carboniferous sedimentary strata, the Pyeon- gan Supergroup, in southern Korea are widely distributed in the Danyang, Taebaeg, Yeongweol, Jeongseon, and Gang- neung areas. The sediments are shallow marine to fluvial in origin and consist predominantly of sandstone and shale with small amounts of carbonate. Cheong (1973) subdivided the Pyeongan Supergroup into the Carboniferous Manhang and Geumcheon formations, the Permian Bamchi, Jangseong, Hambaegsan, Dosagok and Kohan formations, and Triassic Donggo Formation in ascending order. In Danyang area, the Carboniferous strata disconformably cover the Ordovician strata and are divided into two forma- tions, namely, the Manhang and Geumcheon formations (Cheong, 1971) and are inturn unconformably overlain by the Jurassic deposits (Figure 1). Cheong (1971) firstly carried out 50 Jeong-Yul Kim et al. biostratigraphic research on fusulinids in the Danyang area overlies the Ordovician strata. The formation, about 175 m and described 37 fusulinid species belonging to 11 genera. thick, is characterized by red to purple shale and greenish The Carboniferous Manhang Formation unconformably coarse sandstone, with the intercalation of nine white and PO00000000. 7090000008 0099900008 9200099208 RAC 2222227 Ct. = EA CCLOLLO0E. 36° 59' 30" N Cece, Greene 228 2202 Sindanyang 128°22' 30" E Geumcheon Bansong Fm. Em: @ Fossil locality Dosagog Fm. Manhang Fm. Thrust fault | Hambaegsan : Goseong Ls. A Geological boundary GQ” INEmM: sss—- Local road number RE = Jangseong Fm. EF Om Maggol Fm. Figure 1. Geological map and fossil localities of study area. (After Son et al., 1967 ; Lee and Kim, 1995) Carboniferous corals from the Geumcheon Formation, Korea 5] 24 Arachnastraea manchurica Diphyphyllum delicatum Fusulina cylindrica Fusulina sp. Fusulinella mosquensis Fusulinella provecta Ozawainella turgida nN nN Beedeina schellwieni edeina siviniensis Beedeina samarica Beedeina sp. Neostaffella sphaeroidea Geumcheon Formation Manhang Formation CARBONIFEROUS (Moscovian) CARBONIFEROUS (Moscovian) Limestone Chert - bearing limestone Quartz porphyry Soil-coverd Fossil horizon Fault Manhang Formation 125 Unconformity OR. Figure 2. Measured stratigraphic section of study area. light gray limestone beds or lenses in the measured section The Geumcheon Formation from which the coral speci- (Figure 2). In the upper part, the formation contains gray to mens were collected is about 70 m thick and comformably bluish-gray limestone which bears white chert. covers the Manhang Formation. The formation comprises a Jeong-Yul Kim et al. 52 WHOL. ur RN oe N N “ < A TOY we, hy ae ¢ fh, N i ) Carboniferous corals from the Geumcheon Formation, Korea variety of terrigenous sediments intercalated with dark gray limestone lenses (Figure 2). The upper part of the formation is characterized by black shale and greenish sandstone. Abundant and diverse corals and fusulinids were only recor- ded from the limestone units in the formation. Lee and Kim (1995) also described Beedeina schellwieni, Fusulina sp. Neostaffella sphaeroidea, and Ozawainella turgida from the Geumcheon Formation near Gosu Pass in the Danyang area. All of the specimens considered here were collected from a measured section of the Geumcheon Formation exposed in Gosu Pass along the local road 595, Danyang area (Figure 1). The fossil locality 1 is exposed near the top of Gosu Pass, about 1.2km north of the Sindanyang Bridge. The limestone bed of locality 1, which is 2m in thickness, is composed of abundant fusulinids and coral fragments which can not be used in the description. Many kinds of bioclasts, foraminifera, conodonts, brachiopods, and crinoids, were also found from the limestone bed. The fossil locality 2 is about 800m northwest from the Sindanyang Bridge. Fossil specimens were collected from a 5m thick chert-bearing limestone bed which is stratigra- phically nearly 40m above the base of the Geumcheon Formation. The limestone is characterized by gray to dark gray color (Figure 2). Abundant corals together with fusulinids, brachiopods, bryozoa, and crinoid stems are cleary shown on the weathered surface of limestone bed. Systematic description The conventional treatment has been followed in the taxonomic hierarchy above the species level. The mor- phologic terminology used for systematic description fol- lowed is that of Hill (1935, 1956, 1981), the terminology of microstructural elements is that of Kato (1963, 1968). Speci- mens collected for the present study and described herein are housed in the Department of Earth Science Education, Korea National University of Education. Phylum Cnidaria Hatschek, 1888 Class Anthozoa Ehrenberg, 1834 Order Rugosa Milne-Edwards and Haime, 1850 Suborder Streptelasmatina Wedekind, 1927 Family Lithostrotionidae d’Orbigny, 1851 Genus Arachnastraea Yabe and Hayasaka, 1916 Arachnastraea Yabe and Hayasaka, 1916, p. 69. Type species.—Arachnastraea manchurica Yabe and Hayasaka, 1916, from the Lower Permian of South Manchur- ia. Diagnosis.—Corallum compound, massive, typically cerioid or astraeoid. Septa numerous, of two orders. Septa thin, usually extending across tabularium to columella but partly Nn LU) discontinuous in dissepimentarium. Both major and minor septa are well developed. Tabulae conical, complete or incomplete, regular dissepimentarium (slightly modified after Hill, 1956). Remarks.—In the typical species of the Devonian Phillips- astraea d'Orbigny, the septa never extend to the center of the corallites with horse-shoe dissepiments. The septa are dilated, especially at inner margin of dissepimentarium, and there is always a conspicuous inner wall formed by the abrupt thickening of all the septa. These characteristic features are not visible in Arachnastraea (Yabe and Hayasa- ka, 1916). Kato (1972) concluded that Yabe and Sugiyama (1940) misdescribed Arachnastraea as Phillipsastraea in an occurrence from Cheonseongri, Suncheongun, Pyeongan- namdo, Northwest Korea. Arachnastraea manchurica Yabe and Hayasaka, 1916 Figures 3-1; 3-2 Arachnastraea manchurica Yabe and Hayasaka, 1916, p. 69. Material.—KNUE 96201-96216 (KNUEDY Locality 2). Four specimens for this study were collected by the present authors from the measured stratigraphic section (see Figure 2). Description.— Transverse section description : Corallum is astraeoid and composed of nearly equal-sized polygonal corallites which are 4.1-6.6 mm in diameter and have 9-11 major septa. Septa are thin, straight, alternately long and short, and fibronormal in terms of microstructure. Major septa reach the center of the corallite. Corallite walls are almost indistinguishable from septa and dissepiments. In most corallites, the major septa are 2.0-3.5 mm long and minor septa are 0.8-2.4mm long. Minor septa typically extend about 2/3 length of major septa to tabularium wall. Dissepimentarium is formed by 3-5 rows and is 0.3-2.7 mm. Tabularium has a diameter of on average 2.3 mm. Longitudinal section description: Dissepiments are well developed in the peripheral part, elongate in form and not much inclined. Dissepimentarium rather wide, occupying about 2/3 of the diameter of the corallites and consisting of 3-5 rows of dissepiments which are an average of 2mm long. Axial tabellae and periaxial tabellae are similarly in- clined. Diameter of the tabularium varies around the aver- age of 2.2mm, from 1.8 to 3.0mm. In the tabularium, the tabulae adjacent to the dissepimentarium have a slope of 25°-40°. Remarks.—One of the so-called ‘Devonian type corals’ from Cheonseongri described by Yabe and Sugiyama (1940) was reidentified by Kato (1972) as Arachnastraea kaipingensis (Grabau). It was the first record of occurrence of Arachna- straea in Korea. Arachnastraea manchurica differs from Arachnastraea kaipingensis in corallite walls, columella and Figure 3. 1,2. Arachnastraea manchurica Yabe and Hayasaka ; 1, transverse section (7, KNUE 96201), 2, Longitudi- nal section (x 7.5, KNUE 96215). 3-5. Diphyphyllum delicatum Minato and Kato ; 3, transverse section showing both the early and mature stages («8, KNUE 96219), 4, slightly obliquely cut logitudinal section (x7, KNUE 96229), 5, slightly obliquely cut transverse section (X 7, KNUE 96217). KNUE 96199). 6. association of Arachnastraea manchurica and Fusulinella sp. (10, 54 Jeong-Yul Kim et al. dissepimentarium. In the latter the corallum is cerioid- astraeoid and corallite walls are well developed, sharply zigzag and partially depressed. The dissepimentarium of the latter consists of 3-4 rows of regular dissepiments. Family Lithostrotionidae d’Orbigny, 1851 Subfamily Diphyphyllininae Dybowski, 1873 Genus Diphyphyllum Lonsdale, 1845 Diphyphyllum Lonsdale, Hill, 1956, p. 283 ; Hill, 1981, p. 383. Type species.—Diphyphyllum concinnum Lonsdale, 1845. Diagnosis.—Fasiculate corallum, typically without colum- ella. Septa short, continuous in dissepimentarium and amplexoid in tabularium. Columella absent or impersistent. Tabulae convex or flat, with downturned edges. Dis- sepimentarium narrow, composed of one or more rows of small dissepiments (slightly modified after Hill, 1956). Remarks.—The species of Diphyphyllum may have a wide range of variability in terms of the structure, shape and mode of the tabulae. This genus has inner tabulae which are strongly arched, and each arch rests upon the arch below. In addition, Sando and Bamber (1985) mentioned that this genus is very similar to Siphonodenaron, from which it differs by having flat or convex tabulae and by lacking a columella or having a thin, vertically discontinuous one. Armstrong (1970) regarded a smaller group of species, such as Diphyphyllum venosum, Diphyphyllum nasorakensis and Diphyphyllum klawockensis, as having complete tabulae with broad flat tops and downturned edges that extend to the dissepimentarium without touching the lower tabulae. The majority of the descibed species of Diphyphyllum indicated a late Early Carboniferous age (Minato and Kato, 1975). This genus is common in North America and is found exclusively in the shallow-water carbonate lithofacies (Sando and Bamber, 1985). Diphyphyllum delicatum Minato and Kato, 1957 Figures 3-3—3-5 Diphyphyllum delicatum Minato and Kato, 1957, p. 137, text-figs. A-C; Minato and Kato, 1974, p. 56-60. Material.—KNUE 96217-96245 (KNUEDY Locality 2). Only two specimens for this study were collected by the present authors from the measured stratigraphic section (see Figure 2). Description.— Transverse section description : Corallum is compound, fasciculate and dendritic rather than phaceloid. Corallites are circular to subcircular. Corallites are closely adjacent, and are often in contact. Mature corallites range from about 6.7 to 11.4 mm in diameter and possess 18 to 25 major septa. Both major and minor septa are thin, fibronor- mal in terms of microstructure. Major septa are 1.5-2.2 mm in length, protruding 0.2-0.9mm in tabularium, except for some major septa which are 0.9-1.1mm in length. Minor septa are usually confined to adaxial first row of dissepi- ments, rarely protruding into second row of dissepiments, and are 0.25 to 0.38mm in length. Dissepimentarium ranges from 1.1 to 2.2 mm in width and consists of one to three rows of regular dissepiments. Tabularium varies from 41 to 6.4 mm in width and is open without any axial structure. Longitudinal section description : Corallites are cylindrical and rather closely disposed. Dissepimentarium is 0.5 to 1.9 mm wide and consists of one to three rows of inclined, inflated to globose dissepiments. Tabulae are mostly com- plete, slightly concave in central part of the corallite, 4 to 9 in a vertical distance of 5mm. However, they turn down- ward at an average angle of 32° before joining the dissepi- ments. Remarks.—Our specimens differ slightly from Minato and Kato's (1975, pl. 9, figs. 2-6, pl. 10, figs. 1-4) species Diphy- phyllum delicatum, which was described from the Upper Carboniferous Nagaiwa Series of northeast Japan, by having more numerous major septa, a wider dissepimentarium, and a more strongly developed row of dissepiments. Igo and Kobayashi (1980) described a new subspecies, Diphyphyllum delicatum nishitamensis, from the Itsukaichi District, Tokyo, Japan, which is similar to, but not conspecific with Diphy- phyllum delicatum illustrated by Minato and Kato (1975). Igo and Kobayashi (1980) noted that Diphyphyllum delicatum and Diphyphyllum delicatum nishitamensis differ noticeably in the length of major and minor septa. The former is character- ized by short major and minor septa, while the subspecies has longer septa compared with the size of the corallite. As Minato and Kato (1957) mentioned, Diphyphyllum has a long stratigraphic range from the Lower Carboniferous to Permian, but this particular species is confined to the upper part of the Upper Carboniferous Geumcheon Formation in the Danyang area. Discussion One of the purposes of this study is to reexamine the Devonian corals mentioned by Yabe and Suzuki (1955). According to Kato (1972), Suzuki earlier collected several coral specimens in Gosuri, Danyang in 1944, but these materials are lost. Yabe and Suzuki (1955) reported the occurrence of the Devonian corals Disphyllum sp. and Phillipsastraea sp. Their figures 1 and 2 are index maps of the fossil locality, while figures 3 and 4 show the corals on the weathered surface of the limestone near Gosu Pass in Danyang area. The figures are not clear, but colony type and internal structure of corals were, however, distinguished. On the basis of their figure 3, several clues to identification of the corals were found by the present authors. First of all, the corallites in figure 3 are compound, fasciculate and dendritic rather than phaceloid. Although Yabe and Suzuki (1955) identified them as Disphyllum sp., the branches of their coral specimens are too irregular to be those of Disphyllum. The second is that the septa are very short and the dis- sepimentarium are very narrow with one or two rows of small dissepiments. In longitudinal view, the tabulae are convex with downturned edges without columella. These are typi- cal characters of Diphyphyllum. It is considered that the coral specimens described by Yabe and Suzuki (1955) are not of the Devonian genus Disphyllum, but the Carboniferous Diphyphyllum. Disphyllum sp. is illustrated only in figure 3 of Carboniferous corals from the Geumcheon Formation, Korea Yabe and Suzuki (1955), but they did not provide any illustra- tions of Phillipsastraea sp. Furthermore, fusulinids and conodonts occur abundantly from the Geumcheon Formation. A number of fusulinids are observed together with corals in the same thin sections (Figure 3-6). Because the Carboniferous corals have long ranges, both fusulinids and conodonts may provide a useful criteria for understanding the paleoecology and determining the geologic age of the Geumcheon Formation. Conclusion Two species of rugose corals from the Geumcheon For- mation in the Danyang area, Korea are described as Arach- nastraea manchurica and Diphyphyllum delicatum. The corals indicate that the age of the Geumcheon Formation is middle Moscovian, Late Carboniferous. Coral specimens from the Danyang area once illustrated as the Devonian corals Disphyllum sp. and Phillipsastraea sp. (Yabe and Suzuki, 1955), are considered Carboniferous corals, Diphyphyllum sp. and Arachnastraea sp. respectively. Acknowledgments We wish to sincerely thank Makoto Kato, Professor Emeritus of Hokkaido University, and Hisayoshi Igo, Professor Emeritus of the University of Tsukuba for sending useful references and giving comments. We wish to express our thanks to E.W. Bamber, Geological Survey of Canada, Lin Baoyu, Institute of Geology, Chinese Academy of Geological Sciences, Lin Ying Dang, Changchum College of Geology, and Wang Xun Lian, China University of Geosciences, for kindly offering helpful comments and sending many copies of valuable references. Special thanks are given to two anonymous referees for critically reviewing the original manuscript and suggesting numerous useful comments and constructive revisions. References Armstrong, A.K., 1970: Mississippian rugose corals, Per- atrovich Formation, west coast, Prince of Wales Island, southeastern Alaska. U.S. Geological Survey Profes- sional Paper, no. 534, 44 p. Brill, G., 1957 : Geology of Tanyang Coalfield of the Republic of Korea. Geological Report on Coalfields of Korea, vol. 1, p. 75-98. Cheong, C.H., 1971: Stratigraphy and paleontology of the Danyang Coalfield, North Chungcheong-do, Korea. Journal of Geological Society of Korea, vol. 7, p. 63-88. Cheong, C.H., 1972: On the Devonian problem in Korea. Journal of Geological Society of Korea, vol.8, p. 53-54. Cheong, C.H., 1973: A paleontological study of the fusulinids from the Samcheog Coalfield, Korea. Jour- nal of Geological Society of Korea, vol. 9, p. 47-82. Cho, M.J., Choi, Y.S., Kang, P.C. and Choi, K.H., 1986: A study on structural analysis for the southern part of Taebaegsan region. Researches on Coal Resources vol. 5 (KR-86-2-10), p. 239-279. Hill, D., 1935: British terminology for rugose corals. Geo- Un in logical Magazine, vol. 72, p. 481-519. Hill, D., 1956: Rugosa. In, Moore, R.C. ed., Treatise on Invertebrate Paleontology, Part F, Coelenterata, p. 233 324. Geological Society of America and University of Kansas Press, Lawrence. Hill, D., 1981: Rugosa and Tabulata. In, Teichert, C. ed., Treatise on Invertebrate Paleontology, Part F, Coelen- terata, Supplement 1, 762p. Geological Society of America and University of Kansas Press, Lawrence. Igo, H. and Kobayashi F., 1980: Carboniferous corals from the Itsukaichi district, Tokyo, Japan. Science Report, Institute of Geoscience, University of Tsukuba, Section B, vol.1, p. 149-162. Kato, M., 1963: Fine skeletal structures in Rugosa. Journal of Faculty of Science, Hokkaido University, Series 4, vol. 11, p. 571-630. Kato, M., 1968: Note on the fine skeletal structures in Scleractinia and Tabulata. Journal of the Faculty of Science, Hokkaido University, Series 4, vol. 14, p. 45-50. Kato, M., 1972: Devonian of Korea. Journal of Geological Society of Japan, vol. 78, p. 541-544. Kim, H.M., 1971: Paleozoic and Mesozoic paleocurrents of the Danyang Coalfield, Korea. Journal of Geological Society of Korea, vol. 7, p. 257-276. Kim, J.H. and Koh, H.J., 1992: Structural analysis of the Danyang area, Danyang Coalfield, Korea. Journal of Korean Institute of Mining Geology, vol. 25, p. 61-73. 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Journal of Korean Earth Science Society, vol. 16, p. 144-151. Lee, D.W. and Kim, D.S., 1966: Geology of northern part of Danyang Coalfield. Geological Report on Coalfield of Korea, vol. 7, p. 5-32. Minato, M., 1975: Upper Carboniferous corals from the Nagaiwa Series, southern Kitakami Mountains, N.E. Japan. Journal of Faculty of Science, Hokkaido Uni- versity, vol. 16, p. 43-119. Minato, M. and Kato, M., 1957: Two Carboniferous corals from the Kitakami Mountains, northeast Honshu, Japan. Transactions and Proceedings of the Palaeontological Society of Japan, New Series, no. 28, p. 137-142. Park, S.I. and Cheong, CH, 1975: A study on the Jurassic Sapyeongri Conglomerate in the vicinity of Danyang, N. Chungcheongdo, Korea. Journal of Geological Society of Korea, vol. 11, p. 24-37. Park, J.S., Shin, M.S., Chung, C.S., Lee, M.H., Yoon, Y.D., Nn a Kim, S.H. and Hwang, H.S., 1975 : Geological investiga- tion report of Danyang Coalfield. p. 54. Sando, W.J. and Bamber, E.W., 1985: Coral zonation of the Mississippian System in the western interior province of North America. U.S. Geological Survey Professional Paper, no. 1334, 55 p. Son, C.M., Cheong, C.H., Kim, B.K., Lee, S.M. and Kim, S.J., 1967 : Geology of the Danyang Coalfield. Geological Report on Coalfields of Korea, vol. 8, p. 73-94. Jeong-Yul Kim et al. Yabe, H. and Hayasaka, I, 1916: Paleozoic corals from Japan, Korea and China. Journal of Geological Society of Tokyo, vol. 23, p. 9-22. Yabe, H. and Sugiyama, T., 1940: Discovery of corals of Devonian types from Tyosen (Korea). Proceedings of the Japan Academy, vol. 15, p. 305-310. Yabe, H. and Suzuki, A., 1955: Second occurrence of colonial coral of Devonian type in Tyosen (Korea). Proceedings of the Japan Academy, vol. 31, p. 355-359. Cheonseongri KEH, Danyang Fi, Donggo Formation # Gangneung {1 {%, Geumcheon Formation 27)! |/e, Jangseong Formation EE, Jeongseon fig#=, Kohan Formation HE, Manhang Formation Hé Gosu 5 tf}, Dosagok Formation 78-4 Hambaegsan Formation Jak All le EI TES, Pyeongan Supergroup FASIEÉ£, Sindanyang #1}, Taebaeg KH, Yeongweol Fk Paleontological Research, vol. 3, no. 1, pp. 57-64, 6 Figs., April 30, 1999 © by the Palaeontological Society of Japan Relation of growth rings to reproductive cycle in Cryptopecten vesiculosus, a dimorphic pectinid bivalve NAOKO TAKENAKA Shinagawa Joshi Gakuin, 3-3-12 Kitashinagawa, Shinagawa-ku, Tokyo 140-8707, Japan Received 30 October 1998 ; Revised manuscript accepted 23 February 1999 Abstract. The relation between growth rings and reproductive cycle in a dimorphic pectinid bivalve, Cryptopecten vesiculosus (Dunker, 1877) was examined histologically on the basis of semi-regularly collected samples from Sagami Bay. This pectinid is hermaphroditic. Male and female gonads ripen between June and September, and spawning occurs during July to November. A strong growth ring is formed just before spawning, and the first ring indicates that the specimens has reached the stage of sexual maturity. This means that growth rings are formed once a year after the individual reaches sexual maturity. No visual difference was detected in the gonad development between the two phenotypes ; their gonadal weight indices are statistically identical throughout the year. Therefore the previous interpretation that the dimorphism represents discontinous intrapopulational variation is upheld. The results of this study are applicable to life history analysis in extant and fossil populations. Key words: Dimorphism, growth rings, life history, pectinid bivalve, reproductive cycle Introduction The pectinid bivalve, Cryptopecten vesiculosus (Dunker, 1877) is characterized by a few prominent commarginal growth rings, which consist of periodic changes in the convexity of the disc surface. It has been judged that the growth rings are caused by a growth pause during the reproductive season. Furthermore, C. vesiculosus has been considered a dimorphic species, because two discrete phenotypes exist in every population. One phenotype has highly elevated and generally quadrate radial ribs, while the other has low and generally rounded radial ribs. They have been called “Phenotype Q” and “Phenotype R”, respectively. These two phenotypes are strictly sympatric, and their allozyme patterns show no statistical difference. Conse- quently it has been believed that the dimorphism is due to discontinous intrapopulational variation (Hayami, 1984 ; Sar- ashina, 1995). Histological observations on the development of gonads through the year is vital to prove the assumptions mentioned above, as well as to trace a clear relation between growth rings and the reproductive cycle. The relation, if clarified, would become fundamental to analyses of life history (espe- cially, age, lifespan, growth rate and mortality rate) not only in extant but also in fossil populations. Material and method Cryptopecten vesiculosus (Dunker, 1877) is distributed from the central part of Japan to the East and South China Sea. It is a lower sublittoral species, living Commonly on sandy bottoms at the depth of 50-200 m (Hayami, 1984). Fossils of this species are also found abundantly in Early Pliocene and later marine deposits of Japan. Living individuals of C. vesiculosus were collected monthly to bimonthly between March 1997 and February 1998 almost at one and the same station, about 2 km west of the western end of Jögashima Islet in the eastern part of Sagami Bay [35°08’N, 139°35’E, 80-85 m]. Table1 shows the dates of dredging and the number of collected living individuals. The integrated rela- tive frequency of the two phenotypes is almost identical with the ratio indicated by Hayami (1984) in samples Jg (1-26) collected during 1974-1983 at nearby stations in Sagami Bay, and statistically there is no significant difference. To clarify the reproductive cycle and the shell size at sexual maturity, | observed the process of gametogenesis and determined the gonad developmental phase for many individuals in each phenotype. Collected specimens were anesthetized with 0.01% 2-phenoxyethanol methylene glycol diluted with sea water, and then fixed for 48 hours in a solution of 10% formaldehyde. The dissected gonadal tis- sue of each specimen was excised and weighed after rinsing in water. It was dehydrated through a graded series of ethanol and benzol, and then embedded in paraffin (melting 58 Table 1. Collecting dates and the number of individuals of Cryptopecten vesiculosus. Date Na Nea N P Op Mar. 25, 1997 9 14 23 0.61 0.10 May 1, 1997 42 30 72 0.42 0.06 Jun 4, 1997 26 25 51 0.49 0.07 Jul. 29, 1997 54 30 84 0.36 0.05 Sep. 30, 1997 79 67 146 0.46 0.04 Nov. 19, 1997 35 28 63 0.44 0.06 Dec. 18, 1997 44 31 75 0.41 0.06 Feb. 16, 1998 36 36 72 0.50 0.06 Total 325 261 586 0.45 0.02 N: Total number of individuals ; No: Number of individuals belonging to Phenotype Q; Nr: Number of individuals belonging to Phenotype R; P=Nr/N; op: Standard error. point: 56~58'C). Thin transverse sections of the gonadal tissue were prepared at intervals of 8 um and stained with Lillie-Mayer's hematoxylin-eosin. The stained thin sections were observed and photographed using an Olympus model BX50 optical microscope. Based on histological examina- tion of the thin-sectioned gonadal tissue, each specimen was assigned to a specific gonad developmental phase : early active phase (EA), late active phase (LA), ripe phase (R), partially spawned phase (PS), or spent phase (S). Further, the mean gonad index [(gonad weight 100)/soft body weight] was calculated for sexually mature individuals to analyze the annual reproductive cycle of the population. The results were analysed to determine whether or not growth rings can be used as an index of age. Shell height from the umbo to each growth ring, normal to the hinge line, was measured in all the samples with a digimatic caliper (accuracy+0.02 mm). In addition, the numbers of growth rings was counted, and the mean shell height at each growth ring was calculated for individuals with more than three growth rings. The fit of these mean values to von Bertalanf- fy, Gompertz and logistic curves was examined. These Curves are expressed by the following formulae : H(B)=K(1— expla—Rt)) (von Bertalanffy curve) H(G)= Kexp(— aexpfRt) (Gompertz curve) H())=K /(1+ exp(a— Rt)) (logistic Curve) where H is the size of the animal (Shell height in this case) at age t, K is the upper limit of the curve, R is the specific growth rate, and a is a constant defined by the initial size (=H,) at t=0. Naoko Takenaka Results 1. The reproductive cycle of Cryptopecten vesiculosus Spermatozoa were observed in the milky white proximal part of the crescentic gonad and oocytes in the orange distal part. In consequence, it was confirmed that Cryptopecten vesiculosus is hermaphroditic and that the shell dimorphism is never sexual. Histological examination of gonadal tissue revealed that gametogenesis in C. vesiculosus is essentially similar to that in the commercial scallop Azumapecten farreri nipponensis, which was analyzed by Kanno and Tanita (1961), though that species is dioecious. Following the general classification of gametogenetic phases in bivalves proposed by Ropes (1968) and Sato (1995), the reproductive cycle of C. vesiculosus is described below. Early active phase (Figure 1A, B) In the male gonad of this phase, many spermatogoniums about 8 um in diameter, each of which consists of a nucleus and thin nucleoplasm, appear along the inner periphery of the alveolar walls. Further, spermatocytes about 5 um in diameter proliferate towards the lumina from the alveolar walls. Oogoniums and oocytes which protrude inside the alveolar walls are seen in the female gonad. The oogoniums range from 15 to 20 um and the oocytes range from 20 to 30 um in diameter. Each oocyte has a nucleus about 15-20 4m, which contains a nucleolus approximately 4 um in diameter. Late active phase (Figure 1C, D) Many spermatocytes are seen in the male gonad of this phase. Spermatids about 4.5 um in diameter also are seen, and they form dense masses near the center of the alveoli. A transformation of the spermatids results in the appearance of sperm. They form weak columns toward the center of the alveoli. Oocytes in the late active phase are mostly rounded and larger than in the early active phase. Some oocytes are attached to the basement membrane of the alveoli, but most are free in the lumina. In this phase oogoniums and ripe oocytes coexist within one and the same female gonad. Ripe phase (Figure 1E, F) In this phase, spermatozoa or free oocytes occupy the major space in the gonadal tissue. The head of each sperm is corn-shaped and about 2 wm in length. Oocytes are free in the lumina of the alveoli. Each oocyte about 60 um in diameter contains a round or oval nucleus ranging from 30 to 35 um, and each nucleus possesses one small opaque basophilic nucleolus about 5 um in diameter. Ripe gonads typically have a dense appearance because the alveoli are crowded together and are filled with large oocytes or numer- Figure 1. Optical photomicrographs of sections of male and female gonadal tissues in Cryptopecten vesiculosus in each phase of the reproductive cycle. The scale bar in A pertains as well to B-J. All specimens were collected from Sagami Bay. A: Early active phase of a male collected on 16 February 1998. B: Early active phase of a female collected on 16 February 1998. C: Late active phase of a male collected on 25 March 1997. D: Late active phase of a female collected on 25 March 1997. E: Ripe phase of a male collected on 29 July 1997. F: Ripe phase of a female collected on 29 July 1997. G: Partially spawned phase of a male collected on 19 November 1997. H: Partially spawned phase of a female collected on 19 November 1997. a female collected on 18 December 1997. 1: Spent phase of a male collected on 18 December 1997. J: Spent phase of Relation of growth rings to reproductive cycle in Cryptopecten vesiculosus 59 60 Naoko Takenaka ous spermatozoa. Partially spawned phase (Figure 1G, H) In the male gonad of this phase, spermatozoa are still present near the center of alveoli, but they are substantially less numerous than in the ripe phase. A few large ripe oocytes remain free in the lumina of some alveoli of the female gonad. Spent phase (Figure Il, J) In this phase the alveoli of male and female gonads contain few or no spermatozoa or oocytes. Their lumina characteristically are open. Seasonal change in the relative frequency of the five gametogenetic phases in the samples of Cryptopecten vesiculosus from Sagami Bay in 1997-1998 is shown in Figure 2. Individuals belonging to the late active phase amount to than 80% of the population between March and May, while ripe-phase individuals become dominant between June and September. Some individuals begin to spawn in July, and almost all individuals reach the spent phase in December. After that, the proportion of individuals in the early active phase increases gradually. The mean Phenotype Q 100 90 80 70 60 50 Frequency (%) Phenotype R 100 90 80 70 60 50 Frequency (%) MSASMEU UN AS SN ONNEDAURENM Month Figure 2. Diagram showing the change of relative fre- quency (%) of gonad development stages through a year (1997-1998) in the two phenotypes of C. vesiculosus. EA: Early active phase, LA: Late active phase, R: Ripe phase, PS: Partially spawned phase, S: Spent phase. pO mm ————— Fee 30 % Phenotype Q 25 % Phenotype R i ‘ | ait $ 0 Mean gonad index (%) MONA MS JA JEANS 0) IN Si Dia eel Month Figure 3. Seasonal changes in mean gonad _ index |(gonad weight x 100)/soft body weight]. The mean and the range of one standard deviation (vertical bar) are indicated. No statistical difference was detected between the two phenotypes. gonad index increases from March to June, scarcely changes from June to September, and decreases significant- ly after September (Figure 3). Therefore, the reproductive season of C. vesiculosus is considered to be a relatively long period between early June and late September. Neither visual nor statistical difference was detected between the two phenotypes in their reproductive cycles and seasonal changes of gonad indices. 2. The size at sexual maturity Table 2 indicates the frequencies of juvenile, semimature and mature specimens and their relation to shell height in the samples collected during the reproductive season. Repro- ductive cells were not observed at all in individuals smaller than 10 mm in shell height, and gonadal tissue, if present, was so small that they are regarded as juvenile. Individuals larger than 14 mm in shell height can be regarded as mature. Most individuals between 10 and 14 mm possess only a few reproductive cells. They are regarded here as semimature, and spawn like mature individuals. It is, therefore, consid- ered that individuals of C. vesiculosus reach sexual maturity at about 10 mm in shell height. 3. Formation of growth rings The position of growth rings was observed, and the follow- ing four states are discriminated by the relation between the last growth ring and the ventral margin (Figure 4). State A (Figure 4-1a, 1b) Individuals with swelling of the marginal area State B (Figure 4-2a, 2b) Individuals with a growth ring just on the ventral margin State C (Figure 4-3a, 3b) Individuals with slight new shell growth (<5 mm) after the formation of last ring State D (Figure 4-4a, 4b) Individuals without swelling of the marginal area The seasonal change in the relative frequency of these states is shown in Figure 5. In spring, many individuals in Relation of growth rings to reproductive cycle in Cryptopecten vesiculosus Table 2. Distribution of the stages of sexual maturation in relation to shell height in the samples of Cryptopecten vesiculosus collected from Sagami Bay during the reproductive season. Shell Sampling date height May 1 June 4 July 29 Sept. 30 Nov. 19 (mm) A B Gc A B C B C A B C A B C 6- 8 8-10 1 10-12 1 12-14 1 2 12 14-16 16-18 6 18-20 9 1 20-22 11 22-24 2 24-26 1 26-28 A: Juveniles, B: Semimature individuals, C: Mature individuals A 1 1 1 SO ORONUI— — — Woah © @ N © Figure 4. Extant sample of Cryptopecten vesiculosus collected from Sagami Bay. 1: Individual of Phenotype Q with swelling of marginal area (State A) collected on 1 May 1997, (a) right view, (b) anterior view ; 2: Individual of Phenotype R with a growth ring just on ventral margin (State B) collected on 30 September 1997, (a) right view, (b) anterior view; 3: Individual of Phenotype Q with slight new growth (<5 mm) after the formation of the last growth ring (State C) collected on 16 February 1997, (a) right view, (b) anterior view ; 4: Individual of Phenotype Q without swelling of marginal area (State D) collected on 25 March 1997, (a) right view, (b) anterior view. All figures magnified about 1.9 times. 61 62 Naoko Takenaka Frequency (%) M A M J J AS O N D JS F M Month Figure 5. Diagram showing the relative frequency (%) of four states of shell growth. State A : Individuals with a swelling of the marginal area, State B: Individuals with a growth ring just on the ventral margin, State C : Individuals with slight new growth (<5 mm) after the formation of the last growth ring, State D: Individuals without swelling of the marginal area. state A appear simultaneously with the early development of the gonads. Individuals in state B become most abundant in July. This produces a temporary cessation of shell growth. On the other hand, the proportion of individuals in state C gradually increases from June and becomes almost 100% in November. The result indicates that the growth rings are formed once a year and can be used as an index of age. The shell height at each growth ring was measured in all individuals (Figure 6). The first growth ring is formed at a height of 9-11 mm in most individuals. Using individuals with more than three growth rings, | calculated the mean shell height at each growth ring. | then examined how the data adapt to the von Bertalanffy, Gompertz and logistic growth curves. The results of Computation show that the shell growth of this species fits well to all of the three curves, especially to the Gompertz curve (Table 3). 90 | _ 80 @ Ist growth ring © 2 70 O 2nd growth ring 2 60 03rd growth ring = 50 & 4th growth ring © Sa © 30 5 20 zZ ei hile 0 Domo. =. n®»oor un» Do Fr ® OO or NO STM OR el ll reereerer NNNNNNAN LOSC UE et: 12! RUMI CL anes Clee TE RER Ne ite ne Ope eNO Sh ON OEM DO EO MEN Oot ste 10 DO ete ler N) peg se NNNNNNANWN Shell height at the growth ring (mm) Figure 6. Frequency distribution of shell height at each growth ring in the samples of Cryptopecten vesiculosus col- lected during March 1997-February 1998. Table 3. Mean shell height at each growth ring and its adaptability to three theoretical growth curves of the extant sample of Cryptopecten vesiculosus collected from Sagami Bay. Age (years) 1 2 3 4 Mean shell height (mm) Standard deviation Number of individuals 337 176 47 5 Calculated values (mm) von Bertalanffy curve 10.20 1750 21.80 24.35 Gompertz curve 10.20 1743 21.98 24.30 logistic Curve 10.20 17.41 2216 2416 Calculated formula curve von Bertalanffy curve H(B)= 28.02 (1 — exp (—0.453—0.527t)) r=0.999 Gompertz curve H(G)= 26.24 exp (— 2.180 exp 0.8371) r=1.000 logistic Curve H(l) = 25.16/(1 + exp (1.574—1.192t) r=0.998 Discussion The spawning season of Cryptopecten vesiculosus begins in early June and extends to late September, continuing for a comparatively long period. No visual difference was detected in the gonad development between the two phenotypes ; seasonal changes of weight indices of the gonads show very similar patterns (Figure 3). Therefore, the previous interpretation that the dimorphism is due to dis- continous intrapopulational variation is upheld. Growth rings are formed clearly on the shell surface in many bivalves and are often useful in determining the age of individuals and their growth rate. Kennish (1980) called the strong internal growth lines of bivalves growth breaks. The growth breaks reflect various enviromental or physiological stresses such as freeze shocks (in winter), heat shocks (in summer), thermal shocks, shell-margin abrasions, spawning, neap tides, and storms. There is often a direct relationship between internal growth breaks and external growth rings (Dillon and Clark, 1980). Therefore, growth rings are consid- ered to be formed by the same factors as internal growth breaks. Among various bivalves, growth rings are produced by freeze-shock breaks (e.g., Pecten maximus, Mason, 1957 ; Tivela stultorum, Hall et al., 1974; Modiolus modiolus, Seed and Brown, 1978; Aequipecten opercularis, Broom and Mason, 1978; Mya arenaria, Goshima, 1982; Phacosoma japonicum, Tanabe, 1988) or heat-shock breaks (e.g., Mer- cenaria campechiensis, Jones et al., 1990 ; Chamelea gallina, Ramon and Richardson, 1992). Spawning breaks are also used to assess annual growth increment in some species (e. g., Spisula solidisima, Jones et al., 1978; Arctica islandica, Thompson et al., 1980). Generally, a growth ring is formed by an interruption of the shell growth. Because various states of the ventral margin are observed within each simultaneous sample of C. vesiculosus, it is unlikely that growth cessation due to ther- mal stress or any other such instantaneous events. Relation of growth rings to reproductive cycle in Cryptopecten vesiculosus 63 The cause of ring formation may be better understood, if gametogensis and spawning are taken into consideration. Some individuals of C. vesiculosus begin to spawn in July, but the spawning season extends until the end of September (Figure 2). Moreover, the number of individuals with newly grown shell after the formation of the last growth ring gradually increases from June on (Figure 5). Consequently, it is obvious that a growth ring is formed just before spawn- ing, when the gonad is still filled with sperm and free oocytes. On the other hand, the gonad index becomes much smaller in individuals with newly grown shell. Reproduction is one of the most energy-consuming physiological activities ; it is therefore likely that gametogenesis exerts a great influence on shell formation. In this connection Gutsell (1930) discussed the formation of growth rings in Argopecten irradians. He believed that a decline of metabolic activity, which is related to the develop- ment of eggs and sperm rather than spawning, must be responsible for the growth cessation. It is considered that the growth ring of C. vesiculosus is also formed by growth cessation in relation to energy consumed in gametogenesis. The surface swelling before the formation of a growth ring may be caused by the retardation of shell growth. The growth rings of C. vesiculosus must be produced just before spawning. The present interpretation is in agreement with the trade-off relationship between somatic and reproductive cells. Since mature reproductive cells were observed in the individuals larger than 10 mm in shell height, sexual maturity may be attained at this size. The first growth ring is com- paratively weak and is formed at 9-11 mm in shell height in most individuals (Figure 6). This is consistent with the sexual maturity size. Therefore, the growth rings of C. vesiculosus are considered to be formed once a year after the individual has reached sexual maturity. The growth rings are thus useful for determining the age of extant specimens and can presumably be applied to fossils as well. The shell growth pattern fits well with the von Bertalanffy, Gompertz and logistic curves. The shell height indicates a decrease in specific growth rate as the shell size approaches its upper limit of 26-28mm. The number of growth rings indicates that the maximum lifespan of C. vesiculosus is four or five years. The absolute growth pattern, however, may change geo- graphically and chronologically within one and the same species. In fact, the growth rate and ultimate size in the samples from Sagami Bay are significantly smaller than those of some other extant and fossil samples, as shown by Hayami (1984, fig. 7). The exact age distribution and mortal- ity rate are difficult to obtain from the present samples, because juvenile individuals smaller than 10 mm in height are not present in most samples and may have passed through the mesh of the dredging gear. It is also not clear whether the first ring is formed during the first year. However, the relation between growth rings and the reproductive cycle has been made very clearer through the present study. Such prominent growth rings occur in some other pectinids ; e.g. Swiftopecten swiftii, Chlamys cosibensis (a fossil species), and Decatopecten striatus. Although more detailed study is necessary for each species, the mode and periodicity of growth rings are very similar in these species to those of C. vesiculosus. It is likely that gametogenesis is related to the formation of growth rings in those species also. It is expected that applying the knowledge about growth rings will clarify the life history of fossil populations and their evolution. On the other hand, in many other pectinids periodical growth breaks, if present, are scarcely accompanied by surface swelling. Even in C. vesiculosus, Pleistocene fossil populations generally show weaker surface convexity between growth rings than the extant populations. The most plausible explanation in my mind is that the degree of trade-off between the gametogenesis and body growth actually varies among the pectinids species. In other words, the prominent growth rings in the extant populations of C. vesiculosus may be the product of more exhaustive trade-off than in many other pectinids and in the fossil populations of this species. Acknowledgments | express my sincere thanks to Itaru Hayami, Kanagawa University for his valuable advice and reading of the manu- script. | am grateful to Shinichi Sato, National Science Museum, Tokyo for his valuable suggestions throughout this study. | also thank staff members of the Geological Institute and Misaki Marine Biological Laboratory of the University of Tokyo for collecting samples. References Broom, M.J. and Mason, J., 1978: Growth and spawning in the pectinid Chlamys opercularis in relation to tempera- ture and phytoplankton concentration. Marine Biology, vol. 47, p. 277-285. Dillon, J.F. and Clark, G.R.ll, 1980 : Growth-line analysis as a test for contemporaneity in populations. /n, Rhoads, D.C. and Lutz, R.A. eds., Skeletal Growth of Aquatic Organisms, p. 395-415. Plenum Press, New York. Dunker, W., 1877 : Mollusca nonnulla nova maris japonici. Malacozoologische Blatter, Bd. 24, p. 67-75. Goshima, S., 1982: Population dynamics of the soft shell clam, Mya arenaria L., with special reference to its life history pattern. Publication of the Amakusa Marine Biological Laboratory, vol. 6, p. 119-165. Gutsell, J.S., 1930 : Natural history of the bay scallop (Pecten irradians). Bulletin of the United States Bureau of Fisheries, vol. 46, p. 569-632. Hall, C.A.Jr., Dollase, W.A. and Corbato, C.E., 1974: Shell growth in Tivela stultorum (Mawe, 1823) and Callista chione (Linnaeus, 1758) (Bivalvia): annual periodicity, latitudinal differences, and diminution with age. Palaeogeography, Palaeoclimatology, Palaeoecology, vol. 15, p. 33-61. Hayami, |, 1984: Natural history and evolution of Cryptopecten (a Cenozoic-Recent pectinid genus). University Museum, University of Tokyo, Bulletin, no. 24, p. 1-149. Jones, D.S., Quitmyer, LR., Arnold, W.S. and Marelli, D.C., 64 Naoko Takenaka 1990: Annual shell banding, age, and growth rate of hard clams (Mercenaria spp.) from Florida. Journal of Shellfish Research, vol. 9, p. 215-225. Jones, D.S., Thompson, |. and Ambrose, W., 1978: Age and growth rate determinations for the Atlantic surf clam Spisula solidissima (Bivalvia: Mactracea), based on internal growth lines in shell cross-sections. Marine Biology, vol. 47, p. 63-70. Kanno, H. and Tanita, S., 1961: Studies on Chlamys farreri nipponensis Kuroda. ll. Seasonal change of the gonads. Bulletin of Tohoku Regional Fishery Labora- tory, no. 19, p. 135-141. Kennish, M.J., 1980: Shell microgrowth analysis. Mer- cenaria mercenaria as a type example for research in population dynamics. In, Rhoads, D.C. and Lutz, R.A. eds., Skeletal Growth of Aquatic Organisms, p. 255-294. Plenum Press, New York. Mason, J., 1957 : The age and growth of the scallop, Pecten maximus (L.), in Manx waters. Journal of the Marine Biological Association of the United Kingdom, vol. 36, p. 473-492. Ramon, M. and Richardson, C.A., 1992 : Age determination and shell growth of Chamelea gallina (Bivalvia: Vener- idae) in the western Mediterranean. Marine Ecology. Progress Series, vol. 89, p. 15-23. Ropes, J., 1968: Reproductive cycle of the surf clam, Spisula solidissima, in offshore New Jersey. Biological Bulletin, vol. 135, p. 349-365. Sarashina, |., 1995: Genetic variation within a dimorphic species, Cryptopecten vesiculosus (Bivalvia, Pectinidae). Transactions and Proceedings of the Palaeontological Society of Japan, N.S., no. 180, p. 203- 207. Sato, S., 1995: Spawning periodicity and shell microgrowth pattern of the venerid bivalve Phacosoma japonicum (Reeve, 1850). The Veliger, vol. 38, p. 61-72. Seed, R. and Brown, R.A., 1978: Growth as a strategy for survival in two marine bivalves, Cerastoderma edule and Modiolus modiolus. Journal of Animal Ecology, vol. 47, p. 283-292. Tanabe, K., 1988: Age and growth rate determination of an intertidal bivalve, Phacosoma japonicum, using internal shell increments. Lethaia, vol. 21, p. 231-241. Thompson, D.S., Jones, D.S. and Dreibelbis, D., 1980: Annual internal growth banding and life history of the ocean quahog Arctica islandica (Mollusca: Bivalvia). Marine Biology, vol. 57, p. 25-34. a Le ee om \ Os 148 EIAlZ1&, 1999 Æ 6 A 26H (£68 27 A (A) iz, [KREANTACHADEMEE T BRS EST. SRSRHOM LAS 5 A7 ACT. 6A 2 AY Y RY IL [AKON I 0 De, tr: NEBEN TECS, AMPOROMRDREL WHAM DS OED, HDLErÉREN2ELAHESNI HIER ARS (http:// N ammo.kueps.kyoto-u.ac.jp/palaeont) DERAZDON—- PIED-HIHERKÄANTOET, i ©2000 FREI, 2000441 28H SJ-1AS0H (A) ce SAS CHHÉSNET, YO Den It 1009 EIQA BA, YU RYT ADAP LA AUX 1999 Æ az ı O58 149 IPS (FARE T ERA : 2000 FO 6 AREA) ıcık, [ZAR YORE | 7» 5 Bee FA LAADE D ELE, | Of ERST, 2001 FS OER + RL PAO PRIOR DUE SE Lic, PR HE ; SILO A FADS 7 AOMOHA HEOPISOMEED), BIS 1 A PADS 2 ADMD ER + ‘ + % + FOES RZOFERHN) BHÉ&NET, RR TES NCO SRS) LAS, BAL AA Fat, ARBOR LIASSE: T240-0067 ker EHRE 79-2 BEENTA SAR AREA ARE FIRE (TEA) AeGt5e FAIBME—: TEL 045-339-3349 [83H FAX 045-339-3264 FHREREZ E-mail majima@ed.ynu.ac.jp HDA01631 @nifty.ne.jp BE À| (TEARS): T250-0031 / HET A EH 499 HSS) [WRT AR AO aE + HERE ORE TEL 0465-21-1515 FAX 0465-23-8846 E-mail taru @ pat-net.or.jp rer Tr ee EEE OOOO OS OO OS OF OO OE SOOO SL SO OE SOOO OL OL OOOO OO OOS AEEOFAT ICES SAAS, SRDRÉADUHE, SEEMS OAS S 5 NEN ZA DZAMBZATONTOET HEDENZALTEDEN CT. YEAY ST BRASH Ballen RENTE EAN Ae fe wMARMMBRARAH FA rı vv NL R FE eR Ks H ÉEYXLÉROBMEÉS Sa-VY7LN- IRRE (74 7 TT IB) 4 A Ft OMREE SHAM HARRAH) Ick 2, Je ccs, ea eS 19994 4A 27H El hil 113-8622 SEH ABICHK ABSA 5-16-9 1999E4A30H % fr HAMARB LY I-A eas On 3 — 58: A558 ff À À NE - kh - 1 À kB eee Bm - £ - BHR kK an ÉD Al 4 T984-001 (ATK T © Era 8-45 2,500 F fEACAREU MISH ER SEF Att 022-288-5555 HEHE 03- 3455-4415 ISSN 1342-8144 Paleontological Research Paleontological Research Vol. 3 No. 1 April 30, 1999 CONTENTS Keiji Nakazawa: Permian bivalves from West Spitsbergen, Svalbard Islands, Norway .............- Takeshi Setoguchi, Takehisa Tsubamoto, Hajime Hanamura and Kiichiro Hachiya: An early Late Cretaceous mammal from Japan, with reconsideration of the evolution of tribosphenic molars .. .. Kenichi Saiki: A new cheirolepidiaceous conifer from the Lower Cretaceous (Albian) of Hokkaido, Japan ce se kbc sn ee Shwe. ads ale heim ale ae Gallas ee Ser erty cu He dog A Oe Tatsuro Matsumoto and Akitoshi Inoma: The first record of Mesoturrilites (Ammonoidea) from Hokkaido (Studies of the Cretaceous ammonites from Hokkaido and Sakhalin-LXXxIll) .. .. ..... .. Shuji Niko, Yoshitaka Kakuwa, Daisuke Watanabe and Ryo Matsumoto: Early Silurian actinocerid and orthocerid cephalopods from the Kerman area, East-Central Iran Jeong-Yul Kim, Hyonyong Lee and Chang-Hi Cheong: Occurrence of Carboniferous corals from the Geumcheon Formation of Danyang area, Korea .. .. .. ke 22 22 ce ee ee ce en ee an en en en an en te en ee Naoko Takenaka: Relation of growth rings to reproductive cycle in Cryptopecten vesiculosus, a dimorphic pectinidibiIVAIVE: faux u. on esse ee Gales 40) SR oe oa eee 18 29 36 ai 49 57 Paleontological Research Por ISSN 1342-8144 E: u Formerly Y254 : 3 Transactions and Proceedings Va of the Palaeontological Society of Japan Vol. 3 No.2 June 1999 The Palaeontological Society of Japan Co-Editors Kazushige Tanabe and Tomoki Kase Language Editor Martin Janal (New York, USA) Associate Editors Jan Bergstrom (Swedish Museum of Natural History, Stockholm, Sweden), Alan G. Beu (Institute of Geological and Nuclear Sciences, Lower Hutt, New Zealand), Satoru Chiba (Tohoku University, Sendai, Japan), Yoichi Ezaki (Osaka City University, Osaka, Japan), James C. Ingle, Jr. (Stanford University, Stanford, USA), Kunio Kaiho (Tohoku University, Sendai, Japan), Susan M. Kidwell (University of Chicago, Chicago, USA), Hiroshi Kitazato (Shizuoka University, Shizuoka, Japan), Naoki Kohno (National Science Museum, Tokyo, Japan), Neil H. Landman (Amemican Museum of Natural History, New York, USA), Haruyoshi Maeda (Kyoto University, Kyoto, Japan), Atsushi Matsuoka (Niigata University, Niigata, Japan), Rihito Morita (Natural History Museum and Institute, Chiba, Japan), Harufumi Nishida (Chuo University, Tokyo, Japan), Kenshiro Ogasawara (University of Tsukuba, Tsukuba, Japan), Tatsuo Oji (University of Tokyo, Tokyo, Japan), Andrew B. Smith (Natural History Museum, London, Great Britain), Roger D.K. Thomas (Franklin and Marshall College, Lancaster, USA), Katsumi Ueno (Fukuoka University, Fukuoka, Japan), Wang Hongzhen (China University of Geosciences, Beijing, China), Yang Seong Young (Kyungpook National University, Taegu, Korea) Officers for 1999-2000 President : Kei Mori Councillors : Kiyotaka Chinzei, Takashi Hamada, Yoshikazu Hasegawa, Itaru Hayami, Hiromichi Hirano, Noriyuki Ikeya, Junji Itoigawa, Tomoki Kase, Hiroshi Kitazato, ltaru Koizumi, Haruyoshi Maeda, Ryuichi Majima, Makoto Manabe, Hiroshi Noda, Ikuo Obata, Kenshiro Ogasawara, Terufumi Ohno, Tatsuo Oji, Tomowo Ozawa, Yukimitsu Tomida, Tsunemasa Saito, Takeshi Setoguchi, Kazushige Tanabe, Akira Yao Members of Standing Committee : Hiroshi Kitazato (General Affairs), Tatsuo Oji (Laison Officer, Makoto Manabe (Finance), Kazushige Tanabe (Editor in Chief, PR), Tomoki Kase (Co-Editor, PR), Ryuichi Majima (Planning), Hiromichi Hirano (Membership), Kenshiro Ogasawara (Foreign Affairs), Haruyoshi Maeda (Publicity Officer), Noriyuki Ikeya (Editor, “Fossils”), Yukimitsu Tomida (Editor in Chief, Special Papers), Tamiko Ohana (Representative, Union of Natural History Societies). 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Phone : (978)750-8400, Fax : (978)750-4744, www.copyright.com Cover: Idealized sketch of Nipponites mirabilis Yabe, a Late Cretaceous (Turonian) nostoceratid ammonite. Various reconstructions of the mode of life of this species have been proposed, because of its Curiously meandering shell form (after T. Okamoto, 1988). All communication relating to this journal should be addressed to the PALAEONTOLOGICAL SOCIETY OF JAPAN c/o Business Center for Academic Societies, Honkomagome 5-16-9, Bunkyo-ku, Tokyo 113-8622, Japan Paleontological Research, vol. 3, no. 2, pp. 65-80, 8 Figs., June 30, 1999 © by the Palaeontological Society of Japan Three Ordovician cephalopods from the Jigunsan Formation of Korea CHEOL-SOO YUN Geological Institute Graduate School of Science, University of Tokyo, Tokyo 113-0033, Japan Current adaress. Taegu 702-701, Korea Department of Earth Science, Teacher's College, Kyungpook National University, Received 24 June 1998 ; Revised manuscript accepted 10 February 1999 Abstract. Cephalopod species previously described from the Middle Ordovician Jigunsan Formation of Duwibong type Joseon Supergroup of Baegunsan Syncline, Kangweondo in Korea were re-examined taxonomically based on the type and figured specimens and newly collected ones. Three species, Holmiceras coreanicum (Kobayashi, 1927), Sactorthoceras makkolense (Kobayashi, 1927), and Kotoceras grabaui (Kobayashi, 1927) are described. Each species was restudied and compared with closely related species described by Kobayashi (1927, 1934) ; respective lectotypes are also designated herein. In this study, Sigmorthoceras coreanicum, based on its sigmoidally curved conch, was identified as belonging to Holmiceras which is characterized by the early loosely gyroceraconic shell portion. Sinuitopsis kochirien- sis, previously identified as an Ordovician gastropod, is a juvenile shell of H. coreanicum, judging by the number of the volutions and prominent shell surface. Three species belonging to Sactorthoceras and also Cycloceras taihakuense were regarded, based on the existence or nonexistence of the preserved shell and the imploded internal structure, as junior synonyms of Sactorthoceras makkolense in a broad sense. Kotoceras frechi was rejected as an invalid taxon, since its septal angulation, broader siphuncle and rapid expansion of the conch are characteristics caused by secondary deformation. Key words: cephalopods, gyroceraconic, lectotype, Middle Ordovician, secondary deformation, synonym Introduction Paleontological study of the invertebrate fauna from the Cambro-Ordovician formations in Kangweondo, Korea was initiated by Kobayashi (1927). At that time, he identified three units (fossil beds 13, 14, and 15) as the “Chikunsan fossil beds”. From these beds, he described 16 nautiloid species belonging to 8 genera from the Maggol, Hwarari and Hwang- jiri areas. He mentioned that the cephalopods from the “Jigunsan fossil beds” show an affinity with the Chazyan of North America, while the trilobites and brachiopods show European affinity. Kobayashi (1934) subsequently described a great number of cephalopod fossils which belong to 58 species of 29 genera, revising 11 hitherto described species, and stated that the Jigunsan cephalopod fauna is diagnosed by the age of orthoceroidal divergence in cephalopod macroevolutionary history. Later, Kobayashi (1966) made a comprehensive compilation of the Cambro-Ordovician for- mations and faunas of South Korea and divided the Middle Ordovician sequence of the Duwibong type Joseon Super- group into five cephalopod assemblage zones i.e., Manchuro- ceras, Polydesmia, Sigmorthoceras, orthoceroid, and actinoceroid Zones in ascending order. The Korean Ordovician cephalopods have been studied both taxonomically and biostratigraphically by Kobayashi (1927, 1934, 1966, 1969, 1977a, 1977b, 1978) and have not been revised by any subsequent researcher. The series of Kobayashi's works provides important phylogenetic clues and insight into the Asiatic and worldwide Ordovician paleogeography of fossil cephalopods. However, some Korean cephalopod specimens described by Kobayashi require additional restudy in view of the current knowledge of cephalopod taxonomy. This paper aims to re-examine the systematics and taxon- omy of three Ordovician cephalopod species from Korea on the basis of Kobayashi's (1927, 1934) type specimens and newly collected specimens from the type localities and other new localities. Geological setting The Cambro-Ordovician deposits are widely distributed in Kangweon-do, Korea. They have been divided into five types, based on the lithology and fauna; viz., Duwibong, Yeongweol, Jeongseon, Pyeongchang, and Mungyeong types (Kobayashi et al., 1942). The cephalopod specimens 66 Cheol-Soo Yun LEGEND Ordovician Odj Fault National road e Jikdong SANGDONG 10 km Duwibong Formation Jigunsan Formation Maggol Formation Dumugol Formation Dongjeom Quartzite Geologic boundary Provincial road Fossil localities aia de Gürae "Sodo © | 6 GD : Maggol (MG) er : Sesong (SS) GI : Manhangjae (MH) 127 Ee TAEBAEG e : Sanaegol (SN) : Sorogol (SR) : Dongjeom (DJ) Oo U1 B CO PO — Figure 1. Geologic map of the study area, showing the cephalopod localities. used in this study were collected from the Jigunsan Forma- tion, Upper Joseon Supergroup which extends from east to west in the southern limb region of the Duwibong type Joseon Supergroup of the Baegunsan Syncline (Figure 1). The Jigunsan Formation originally named as the “Chikun- san Shale” by Yamanari (1926), is about 50 m thick, confor- mably covers the Maggol Formation and grades into the overlying Duwibong Formation (Figure 2) This formation can be traced from east and west in the Taebaeg region. The Jigunsan Formation is lithostratigrahically divided into the lower, middle, and upper members. The lower member is essentially non-fossiliferous and consists mainly of black shale containing a little calcareous material; the middle member is composed of “worm-eaten” bioturbated limestone and vermicular shale intercalated by three or four limestone beds, each about 50 cm thick, and has yielded a large number of trilobites ; the upper member consists of lime- stone and bioclastic grainstone with intercalating calcareous shale. The amount of carbonate gradually increases toward the top of the sequence and ultimately grades into the limestone of the Duwibong Formation; this member has yielded a rich cephalopod fauna. The Jigunsan Formation is especially well exposed in the Sanaegol section (Figures 1, 2). It consists mainly of black shales and thin beds of calcareous nodules, in which ortho- cerid and lituitid nautiloids occur. The lower member is almost barren of fossils ; the middle member is characterized by the abundant occurrence of Holmiceras ; the upper member is represented by bioclastic grainstone with inter- calating calcareous shale and contains abundant ormocer- oid cephalopods. According to Kobayashi (1934, 1966), the Jigunsan Forma- tion is correlated with the Llandeilo in the European succes- sion and the Chazy in the American sequence. Shimizu and Obata (1935b) described three graptolite species from the formation and correlated it with the Lower Llandeilian Diplograptus teretiusculus and Nemagraptus gracilis Zones in the Glenklin Shale, England and Pingliang Shale of Gansu Province in North China. Shikama and Ozaki (1969) distin- guished three assemblage zones in the Jigunsan Formation in the Dongjeom area, namely, the Orthis nipponica, Basilicus deltacaudus, and Basilicus yokusensis Zones in ascending order, based on the macrofossils collected by a member of the Yokohama Geologists Club in 1967 (Ozaki and Ogino, 1968). The Jigunsan trilobite fauna has been studied in detail by Lee et al. (1980), who described 15 species belonging to 5 genera and correlated the formation with the Llandeilo to Ordovician cephalopods from Korea 67 Duwibong Fm. Sanaegol Section Sorogol Section Dongjeom Section Upper Member c € = I) mo SI o| € T 3 a © o| = Middle Member ce alle 3| § EE sed ey S| 7 _ Lower Member Maggol Section Sesong Section Manghangjae Section Maggol Fm. = Limestone TS Limestone to bioclastic grainstone 1 CAC ZI=I=] with partings calcareous shale Legend = Shale-parted limestone Varnicularehale = Alternation of shale and ao calcareous nodular bed Warm-eaten limestone =| Shale << No exposure Figure 2. Geological columns of the Jigunsan Formation in the study area, showing the horizons of the cephalopod localities. lower Caradoc interval in Europe. Lee and Lee (1986) established a conodont biozone in the middle and upper parts of the Jigunsan Formation, namely, the Eoplacognathus suecicus-Eoplacognathus jigunsanensis Assemblage Zone. These authors correlated the conodont fauna with the Eoplacognathus suecicus-Acontiodus ? linxiensis Zone of the lower Upper Majiagou Formation in North China and with the Lower to Middle Llanvirn in the European type section. They also suggested that the Jigunsan Formation was deposited in a deep shelf environ- ment, based on the conodont fauna. Materials Most cephalopod specimens described by Kobayashi were collected from Maggol in Korea, where strata indicative of the western part of the Duwibong type Joseon Supergroup are exposed (Loc. 1 in Figure 1). The list of type specimens re-examined in this study is shown in Table1. The ce- phalopod type specimens in Table1 are housed in the University Museum, University of Tokyo (UMUT). Fifty-seven specimens listed in Table2 were used for comparison with Kobayashi's type specimens. These new and unstudied specimens were collected by the present author and K. Tanabe on three occasions during May to August, 1997. All of them were discovered from the Middle Ordovician Jigunsan Formation in Kangweondo, Korea. They are deposited in the Department of Earth Science, Teacher's College, Kyungpook National University (KPE prefix), Taegu, Korea. 68 Table 1. List of cephalopod type specimens which were described by Kobayashi (1927, Cheol-Soo Yun 1934) from the Jigunsan Formation and are re-examined in this study. Registered no. Scientific name Locality Type UMUT PM 8 Sigmorthoceras coreanicum Maggol Syntype UMUT PM 9 Sigmorthoceras coreanicum Maggol Syntype UMUT PM 651 Sigmorthoceras coreanicum Maggol Syntype UMUT PM 6 Sactorthoceras makkolense Maggol Syntype UMUT PM 7 Sactorthoceras makkolense Maggol Syntype UMUT PM 660 Cycloceras sp. Hwangji Syntype UMUT PM 570 Sinuitopsis kochiriensis Hwangji Syntype UMUT PM 571 Sinuitopsis kochiriensis Hwangji Syntype UMUT PM 634 Kawasakiceras densistriatum Maggol Holotype UMUT PM 652 Sigmorthoceras sigmoidale Maggol Holotype UMUT PM 657 Cycloceras taihakuense Maggol Paratype UMUT PM 658 Cycloceras taihakuense Maggol Paratype UMUT PM 659 Cycloceras taihakuense Maggol Holotype UMUT PM 650 Sactorthoceras gonioseptum Maggol Holotype UMUT PM 643 Sactorthoceras shimamurai Maggol Holotype Table 2. List of cephalopod specimens from the Middle Ordovician Jigunsan Formation, Kangweondo, Korea. Species | Locality No. of specimens Holmiceras coreanicum | SN801, SN802, SN809, SN835, DJ500, MH201 32 Sactorthoceras makkolense SN802, SN809, SN835, DJ500 15 Kotoceras grabaui | SR900, SS663, MG343, MG350, MG357 10 Systematic paleontology Subclass Nautiloidea Order Tarphycerida Family Lituitidae Genus Holmiceras Hyatt, 1894 Type species.—Lituites praecurrens Holm, 1891 from the Lower Ordovician (Kundan Stage) of Oland, Sweden. Generic diagnosis.—Lituiticonic with adapically one-volut- ed gyroceraconic and adorally sigmoidal curved shell por- tion; septal necks orthochoanitic ; surface ornamented with growth lines and annulations, forming ventral sinus and lateral salient in the earlier coiled stage and transverse or slightly undulating ones in the later stage. Remarks.—Hyatt (1894) recognized that this genus is characterized by having distinct ventral and dorsal lobes in the ephebic stage, with low, broad, almost staight, lateral saddles. Ancistroceras is most closely allied to Holmiceras, but differs from the latter in having small, tightly coiled whorls and a much more rapidly expanding conch. Sweet (1958) emphasized the sigmoid profile of the shell which is missing in Ancistroceras. Holmiceras has long been an all-but-forgotten genus. However, Flower (1975) added Holmiceras benetti from the Middle Ordovician Table Head Formation in Newfoundland to the two previously known Holmiceras species. Presently, only four species in the world can be referred to Holmiceras ; Holmiceras praecurrens (Holm, 1891), Holmiceras kjerulfi (Brögger, 1882), Holmiceras benetti Flower, 1975 and Hol- miceras coreanicum (Kobayashi, 1927) which is described below. Holmiceras coreanicum from the Jigunsan Formation is a first reliable record of this genus from Asia. Holmiceras coreanicum (Kobayashi, 1927) Figures 3-1a, b, 2a, b; 4-1—10. Orthoceras coreanicum Kobayashi, 1927, p. 181, pl. 18, fig. 6; pl. 19, figs. 3a-c. Orthoceras makkolense Kobayashi, 1927, p. 181, pl. 19, figs. 2a-c. Sigmorthoceras coreanicum (Kobayashi). Kobayashi, 1934, p. 413, pl. 22, fig. 7. Sactorthoceras makkolense (Kobayashi). Kobayashi, 1934, p. 408, pl. 15, fig. 9. Cycloceras sp. Kobayashi, 1934, p. 421, pl. 29, figs. 12, 13. Sinuitopsis kochiriensis Kobayashi, 1934, p. 360, pl. 5, figs. 1-4. aff. Trilacinoceras sp. Ozaki and Ogino, 1968, pl. 3, fig. 3. Holmiceras coreanicum (Kobayashi). Yun, 1998, p. 78, figs. 1c-h. Types.—A sigmoidally curved phragmocone figured by Kobayashi (1927, p. 181, pl. 19, figs. 2a-c) from the Jigunsan Formation of Maggol, Kangweondo, Korea, UMUT PMS9, is here designated as the lectotype (see also Figures 3-1a, b). A slightly curved phragmocone specimen from the same locality, UMUT PMB is also designated as the lectoparatype. Material.—In addition to the above two type specimens, newly collected specimens from the Jigunsan Formation including 9 figured (KPE20001, KPE20002, KPE20003, KPE20004, KPE20005, KPE20006, KPE20007, KPE20020, KPE20026-1, KPE20302) and 23 other specimens were Ordovician cephalopods from Korea 69 examined. Specific diagnosis ——Sigmoidally curved conch with early loosely coiled portion ; body chamber long; circular in cross section ; siphuncular segments somewhat expanded within camera; septal necks orthochoanitic ; no cameral deposits detected ; surface ornamented with prominent annulations and very fine growth lines. Description. —Conch large-sized lituiticone, composed of two different continuous shell portions, namely, early loosely coiled juvenile shell portion (Figures 4-1a-c—4) and later sigmoidally curved adult shell portion (Figures 4-6a, 7, 8). The best preserved specimen, KPE20001 (Figures 4-1a— c), is broken into two portions, but when put together is about 63 mm long; the early juvenile shell portion is loosely coiled, its umbilical opening being 3.2mm across, first Camera pointed anterolaterally, constricted to 1mm at a height of 1.5 mm from the adapical apex, forming a subquadrate outline ; internal structure unknown owing to recrystallization ; septa moderately concave and closely spaced with septal spacing 0.7 mm on the dorsum and 1mm on the venter, gradually increasing adorally ; slightly curved later shell portion, 58 mm long, circular in cross section, its diameter expanding from 7 mm at the adapical end to 15.7 mm at the broken upper end ; siphuncle central, narrow, its width one-eighth of the conch diameter ; siphuncular segments tubular to slightly inflated within camerae ; transverse septal suture and surface an- nulations crossing each other; septal depth smaller than one cameral height on the concave side and larger than that on the convex side; cameral height gradually increasing towards the top from 1.3 mm to 2.9 mm, five camerae equal in length to the conch diameter of 15.9 mm measured at the uppermost camera; septal necks orthochoanitic, attaining 0.5mm at the 3rd septum from the adoral end, occupying about one-third of the cameral height, distinguishable from the connecting ring by means of their thickness, septal suture transverse, but intersecting with annulations ; camera filled with crystalline calcite, no organic deposits detected ; siphuncle lined by endosiphuncular nonsegmental material along the inner siphuncular wall and leaving central narrow siphotube ; surface ornamented with low, narrow annula- tions separated by much broader intergrooves, both of which are covered with very fine transverse growth lines, showing different features during ontogeny, ventral sinus and lateral salients in juvenile coiled stage and then adorally run parallel to transverse axis, 7 annulations in a length equal to the conch diameter at the preserved adoral end, annulation density slightly larger than that of septal one, i.e., 8 growth lines occurring between two annulations. KPE20002 (Figure 4-4) represents a young, possibly embryonic or early postembryonic shell with 10 camerae consisting of endogastrically curved gyroconic phragmocone and subsequent straight body chamber, small, 15.5 mm long, conch diameter rapidly enlarging from 2.2mm near the adapical end to 4.9mm at the base of the living chamber ; siphuncle central, its segments expanded within camerae, constricted at the septal necks ; septal depth corresponding to one cameral height ; siphuncle filled with imported matrix, camera filled with crystalline calcite; surface annulated in longitudinal section, being arranged at intervals of 0.8 mm. KPE20003 (Figure 4-2) judging from the silicone rubber cast, is the external mould of an early coiled shell portion, 17.5 mm long, composed of a loosely coiled embryonic shell portion, its umbilical opening about 3mm across, conch expanding at a rate of 1mm per 4mm; surface ornamented with prominent annulations and transverse fine growth lines, forming ventral and dorsal sinuses, and ventrolateral salients. KPE 20004 (Figure 4-7), a sigmoidally curved phrag- mocone, 85.2mm in length, conch diameter expanding moderately rapidly in the earlier stage from 3.8 mm to 10 mm at a distance of 21mm and more slowly afterwards, conch circular in cross section; siphuncle narrow, central; septal necks orthochoanitic ; cameral height ranging from 1.7 mm to 3mm; septal depth slightly larger than one cameral height ; surface ornamented with primary annulations and very fine growth lines. KPE20005 (Figure 4-5) is a sigmoidally cuved fragmentary phragmocone, 76mm in length, conch diameter gently expanding from 10.2 mm at the adapical end to 22.9 mm at the adoral end; siphuncle subcentral, narrow, occupying one-seventh of the conch diameter ; siphuncular segments slightly inflated within camera, dimensions 2.6 mm in length and 3mm in maximum diameter at the midportion of the segment in the adoral end, constricted to 2.2mm at the septal foramina ; septal necks suborthochoanitic, septa rela- tively deep, exhibiting one and a half of the cameral height ; septal distance varying from 19mm to 2.8mm; nonseg- mental endosiphonal linings along the siphuncular wall, leaving a central tube; surface ornamented with distinct annulations and growth lines. KPE20006 (Figure 4-10) is an external mould retaining well preserved surface ornamentation, consisting of annulations very closely spaced at intervals of approximately 1mm, with ventral sinus formed by each annulus about 2.6 mm in width and about 1.3 mm in length in earlier shell portion, and of much more widely spaced, more prominent transverse an- nulations in later shell and further annulations again becom- ing narrower in gerontic shell, annulations and intergrooves both covered with very fine growth lines. KPE20007 (Figures 4-6a, b) represented by a moderately curved, large-sized adult shell lacking an early coiled por- tion, is 162 mm long of which the body chamber is 57 mm long, adoral portion of phragmocone and body chamber secondarily depressed during fossilization, conch circular in cross section ; its diameter gently enlarging from 19.7 mm at the adapical end to 33.3 mm at a point 74 mm farther up; siphuncle central, narrow, a little more than one-seventh of the conch diameter ; siphuncular segment as long as broad ; surface ornamentation on body chamber partly preserved, comprising annulations and growth lines. KPE20302 (Figure 4-8), 53.5 mm in length, consists of a loosely coiled early shell portion and succeeding sigmoidally curved conch, but an initial chamber is not preserved ; umbilical opening about 2.8 mm across ; moderately expan- ding at a rate of 1mm per 5mm. Remarks.—Sigmorthoceras coreanicum from the Jigunsan Formation of Maggol (Kobayashi, 1927, pl. 18, fig. 6; pl. 19, figs. 3a-c ; 1934, p. 413, pl. 22, fig. 7) is the type species of Sigmorthoceras which has been regarded as a doubtful 70 Cheol-Soo Yun taxon for a long time. Externally, the slightly curved conch was regarded as the diagnostic character by Kobayashi (1934). However, Shimizu and Obata (1935a) regarded the sigmoidal conch shape of specimens of Sigmorthoceras described by Kobayashi as a secondarily deformed Sactor- thoceras makkolense. Such secondary deformation is com- mon in other nautiloid fossils from this region. Flower (1946) stated that Sigmorthoceras is an erratic form deviation, perhaps not worthy of generic status. However, the internal morphology of the sigmoidally curved conch of the present species is identical with that of the type specimens of Sigmorthoceras coreanicum. Based on the identical curvature of all the specimens, the secon- dary deformation conjecture by Shimizu and Obata, (1935a) can be rejected. Thus, Holmiceras coreanicum is revealed to possess a loosely coiled early shell portion and slightly sigmoidal more mature conch. It is well known that secondary deformation and dissolu- tion of shelly matter during fossilization sometimes cause misidentification of fossil taxa. Kobayashi (1934) described Cycloceras sp. from the Jigunsan Formation of Homyeong (p. 421, pl. 29, figs. 12,13), based on the annulated ornamenta- tion. The annulations observed on the ventral portion near the adapical end of the specimen are more broadly spaced than those on the dorsal one. Accordingly, the specimen represents a portion of the shell shifting from the early coiled stage to the sigmoidally curved phragmocone in Holmiceras coreanicum. Furthermore, all the features observed in the longitudinal section agree well with those of Holmiceras coreanicum, although the state of preservation of the internal structure is rather poor. Meanwhile, Kobayashi (1934) described a sinuitid gas- tropod, Sinuitopsis kochiriensis from the Jigunsan Formation of Homyeong, based on two incomplete external moulds (Kobayashi, 1934, p.360, pl.5, figs.1-4). In general, the genus Sinuitopsis consists of a tightly coiled shell with 3 to 4 volutions (Knight et al., 1960, pl. 176, fig. 93-7a, b) and its surface is sculptured by fine growth lines without more raised primary annulations. However, the specimens described by Kobayashi (1934) as “Sinuitopsis” have loosely coiled shells having one volution and lacking the characteristic surface sculpture of true Sinuitopsis. In addition, its surface orna- mentation consisting of ventral sinus and lateral salients is strong evidence to support the contention that the two external moulds belong to Holmiceras. Sactorthoceras makkolense (Kobayashi, 1927) was proposed based on two individuals. One of them (UMUT PM7 ; Figures 3-2a, b), illustrated in Kobayashi (1927, pl. 19, figs. 2a-c) differs from the other specimen (UMUT PM6; Kobayashi, 1927, pl. 18, fig.5; see also Figures 3-4a, b) in having more crowded septa and a narrower siphuncle. Accordingly, the former specimen (UMUT PM7) is dissimilar to the lectotype but has a cameral height of no more than two-thirds the diameter of the siphuncle. Moreover, the conch of the specimen has a slightly curved form, although its siphuncular position is more or less eccentric due to secondary deformation. In these respects, this specimen must also be assigned to Holmiceras coreanicum. Ozaki and Ogino (1968, pl.3, fig.3) figured a single nautiloid, aff. Trilacinoceras sp. from the Jigunsan Forma- tion of Dongjeom. It is represented by an early coiled phragmocone. However, its generic identification may be incorrect because of the less loosely coiled portion of the conch than those in the species of the genus Trilacinoceras. Based on the mode of coiling in the early portion of the conch and the surface ornamentation, this nautiloid is assigned with reservation to Holmiceras coreanicum. Comparison.—In view of the external morphology, this species is closely allied to Holmiceras kjerulfi (Brogger) from the Orthoceras Limestone of the Oslo region, Norway (Brgger, 1882, p. 54, pl. 12, fig. 16), but differs from the latter species by its loosely gyroceraconic volution, somewhat curved cyrtoconic or sigmoidal adoral portion, circular section of the conch and slightly more crowded septa. This species is distinguished from Holmiceras benetti Flower from the Middle Ordovician Lower Table Head Limestone, Newfoundland (Flower, 1975, p. 151, pl. 4, figs. 1-6), which has a more rapidly expanding conch and lacks a sigmoidal adoral shell portion. This species is similar to the Middle Ordovician species Ancistroceras undulatum Boll, 1857 recovered from erratic boulders in northern Germany (Foerste, 1929, p. 272, pl. 41, figs. 3,4) and the Ampyx Limestone in Oslo-Asker district, Norway (Sweet, 1958, p.129, pl. 13, figs. 2,3, 5) in that the early coiled portion and the mode of surface ornamentation are similar to H. coreanicum, but this taxon is quite distinct from the latter in its more slowly expanding conch. Like- wise, Ancistroceras subcurvatum Qi, 1980 from the upper Taiwan Formation, Lower Ordovician, Wuwei, Anhui, China (Qi, 1980, p. 256, pl.1, figs. 1, 2) is similar to this species in general features but also differs from it by its own somewhat more rapidly expanding conch. Occurrence.—This species is known to occur from various localities (SN801, SN802, SN809, SN835, DJ500 and MH201) in the Middle Ordovician Jigunsan Formation. Order Orthocerida Family Sactorthoceratidae Genus Sactorthoceras Kobayashi, 1934 Type species.—Sactorthoceras gonioseptum Kobayashi, 1934 from the Jigunsan Formation of Maggol, Kangweondo, Korea. ~ Figure3. 1a,b, 2a,b. Holmiceras coreanicum (Kobayashi, 1927). 1a,b. A sigmoidally curved phragmocone, lectotype (UMUT PMS9), x 1, 1a: lateral view, 1b: longitudinal section. which is here assigned to Holmiceras coreanicum (Kobayashi), 2a, b. “Sactorthoceras makkolense (Kobayashi)”, UMUT PM7, <1, 2a: lateral view, 2b: longitudinal section. 3a, b. Kotoceras grabaui (Kobayashi, 1927). The best preserved partial phragmocone, lectotype (UMUT PM631), <1, 3a: ventral wew, 3b. adoral view of the septa and siphuncle, venter down. 4a, b. Sactorthoceras makkolense (Kobayashi, 1927). An adoral phragmocone, lectotype (UMUT PM6), 4a: longitudinal section, x1, 4b: enlargement of the same section, x 2. Ordovician cephalopods from Korea 71 72 Cheol-Soo Yun Generic diagnosis.—Straight or slightly Curved longiconic orthoceracone with subcentral siphuncle ; siphuncular seg- ments tubular or slightly expanded within camerae ; cameral height nearly equal to or a little more than siphuncular diameter; no discernible cameral and endosiphuncular deposits; surface smooth or ornamented with closely spaced annulations and very fine transverse growth lines. Remarks.—The genus Sactorthoceras is known from the Middle Ordovician formations in East Asia, Norway and northeastern America. Flower (1941) considered Sactor- thoceras as the ancestor of the ascocerid nautiloids that make up a specialized group having siphuncular segments from orthochoanitic to cyrtochoanitic. Indeed, Sactorthoceras may be not distinguished from Holmiceras when any specimen is found as an adoral broken phragmocone without an early coiled shell portion. How- ever, the longitudinal section through the center of the siphuncle reveals that the siphuncle of Sactorthoceras is always broader and its septal distance is higher than in Holmiceras. The generic assignment of Cycloceras M'Coy is based mainly on the surface ornamentation and not on internal structure. The Group1 of Cycloceras which was divided artificially by Kobayashi (1934) is regarded as belonging to either Sactorthoceras or Holmiceras, because its internal structure and surface ornamentation agree well with the latter genera. Moreover, Sweet (1964) mentioned that “no species other than the type species should be referred to Cycloceras until its type is better known”. Based on present knowledge, the genus Cycloceras may be superseded by Wennanoceras, which was proposed by Chen (1976) for shells having a strongly annulated surface and a central siphuncle. Sactorthoceras makkolense (Kobayashi, 1927) Figures 3-4a, b; 5-1—6; 6-1—4 Orthoceras makkolense Kobayashi, 1927, p. 181, pl. 18, fig. 5; not pl. 19, figs. 2a-c. Sigmothoceras sigmoidale Kobayashi, 1934, p. 414, pl. 21, figs. 1 3. Sactorthoceras gonioseptum Kobayashi, 1934, p. 412, pl. 16, fig. 6 ; pl. 18, figs. 1-3; pl. 20, fig. 9. Sactorthoceras shimamurai Kobayashi, 1934, p. 408, pl. 19, figs. 1 3: Kawasakiceras densistriatum Kobayashi, 1934, p. 397, pl. 14, figs. EXT Cycloceras taihakuense Kobayashi, 1934, p. 420, pl. 22, figs. 1,2; pl. 23, figs. 1-5; pl. 24, figs. 4-6. Sactorthoceras makkolense (Kobayashi). pl. 6, figs. 1, 2. Kim et al., 1986, p. 26, Type.—The type specimen, UMUT PM6, from the Jigun- san Formation of Maggol, Kangweondo, Korea is here designated as the lectotype (Figures 3-4a, b). Material.—15 specimens including seven figured ones (KPE20030, KPE20031, KPE20032, KPE20033, KPE20036, KPE20037, UMUT PM634). Specific diagnosis.—Longiconic orthoceracone ; siphun- cular segments tubular; septal necks orthochoanitic to suborthochoanitic ; cameral height nearly equal to siphun- cular diameter; surface ornamented with low annulations and very fine transverse growth lines. Description.—Conch large-sized longiconic orthocer- acone, enlarging at a rate of 1mm per 8 to 10 mm in conch length ; cross sections of conch and siphuncle subcircular ; ratio of the siphuncular diameter versus conch diameter being 1:9 in KPE20030 (Figure 5-3); siphuncle subcentral, tubular ; septa moderately concave forwards, septal depth nearly two to three times the cameral height, septal distance ranging from 3.3 mm to 5.4 mm, in other words, a little more than or equal to the siphuncular diameter, septal necks orthochoanitic, relatively long, approximately 2mm in KPE20037 (Figure 5-6), bending smoothly toward adapical end and then forming a right angle with septa, septal suture directly transverse ; connecting ring thin, distinguishable from septal neck by its thickness ; in KPE20037 camerae comparatively high, ranging from 3.5mm to 4mm, 7 to 8 camerae in a distance corresponding to the conch diameter ; no cameral or siphuncular deposits detected; surface marked with low, narrow annulations, separated by broader interspaces, both covered with very fine numerous trans- verse growth lines, 7 to 8 per 1mm length, annulations being arranged at intervals of about 2 mm, but fluctuating within a narrow range. Remarks.—Kobayashi (1927) described the present species as follows: “In the middle part of the polished specimen (pl. XVIII, fig. 5) the segmentation is quite abnormal, the double — Figure 4. Holmiceras coreanicum (Kobayashi, 1927). 1a-c. Partial phragmocone steinkern (KPE20001) from SN801, 1a: ventrolateral view, showing the septal suture crossing annulations, 1, 1b: dorsoventral section of coiled embryonic conch, *1.8, 1c : longitudinal section of partial phragmocone made by an acetate peel, showing the details of siphuncle and septa, <1.5. 2. Silicon rubber cast of external mould (KPE20003) from DJ500, showing loosely coiled embryonic shell portion with annulated surface ornamentation, x3. 3. Juvenile shell (KPE20026-1) from MG343, dorsoventral section of the early coiled septated shell portion, x3. 4. Possibly embryonic conch (KPE20002) from SN801, dorsoventral section, showing the phragmocone and subsequent body chamber, 3. 5. Partial phragmocone (KPE20005) from DJ500, longitudinal section, showing details of siphuncule and septa, <1. 6a, b. Moderately curved conch (KPE20007) from SN801, <1. 6a: lateral view. Surface ornamentation is partly preserved on body chamber. 6b: apical view, showing the position of the siphuncle. 7. Longitudinal section of partial phragmocone (KPE20004) from SN801 made by an acetate peel, showing the sigmoidally cuved conch and details of siphuncle and septa, <2. 8. Early coiled and later sigmoidally curved conch (KPE20302) from SN802, 1.5. 9a, b. Partial phragmocone (KPE20020) from SN801, x1, 9a: lateral view, 9b: apical view of septum and siphuncle, showing the position of siphuncle. 10. Partial phragmocone (KPE20006) from DJ500, ventral view, silicon rubber cast of external mould, showing the well developed surface ornamentation, especially ventral sinus of annulations on earlier portion, x 2.5. Ordovician cephalopods from Korea 13 74 Cheol-Soo Yun camerae on one side of the siphuncle corresponding to a single camera on the other....... It may be possibly be due to a pathological state”. However, in the type speci- mens of this species (Figures 3-4a, b), the septa in the adoral portion of the phragmocone are distributed disorderedly here and there. This peculiar shell feature is considered to be an artifact created by recrystallization. As the result of restora- tion, the septa on each side in the each longitudinal section of the lectotype (UMUT PM6) correspond well one to one. This phenomenon is easily found in many cephalopods. For example, Actinoceras bellefontense Foerste and Teichert, 1930 shows a disagreement between septa on both sides owing to the diagenesis of internal components (Foerste and Teichert, 1930, p. 227, pl. 38, fig. 2B). Stridsberg (1990) sug- gested that internal destruction of septa may be caused by implosion due to increasing water pressure during post- mortem sinking. Accordingly, the abnormal camerae obser- ved in the lectotype of Sactorthoceras makkolense may not represent a pathological state during life, but were formed secondarily by taphonomic processes. Taphonomic damage gave rise to other taxonomic prob- lems too. Kobayashi (1934, p. 408, pl. 19, figs. 1-3) proposed Sactorthoceras shimamurai for a specimen with very rapid expansion of the conch, namely, at the rate of 1mm per conch length of 4mm. However, this specimen (UMUT PM643), which is represented by a fragmentary phrag- mocone with the last six camerae being closely spaced and a strongly compressed, large-sized body chamber, does not reflect the real expansion rate of the shell owing to secon- dary deformation of the body chamber and erosion of one side. Furthermore, since the last six camerae indicate the gerontic stage, more widely spaced camerae would be present in the adolescent stage. Consequently, Sactor- thoceras shimamurai is regarded as a junior synonym of Sactorthoceras makkolense. Sactorthoceras gonioseptum from the Jigunsan Formation of Maggol was described by Kobayashi (1934) as having a narrower siphuncle and more crowded septa than Sactor- thoceras makkolense. He also emphasized the angulation of the septa shown in the holotype (UMUT PM650) as a diagnostic character of this species. However, this feature can not be observed in the specimen because of the crushed and distorted condition of the septa along the outer part of the cameral portion. Shell breakage during fossiliza- tion resulted in a pinched septal foramen with curiously angulated septal necks. Apart from the aberrant feature of septal angulation, Sactorthoceras gonioseptum can be regard- ed as a junior synonym of Sactorthoceras makkolense. Kobayashi (1934) established Sigmorthoceras sigmoidale on the basis of a single sigmoidally curved specimen (UMUT PM652). He stated that this species is characterized by more broadly spaced septa and a broader siphuncle than in Sigmorthoceras coreanicum. (Kobayashi (1934) described the shell surface of this specimen as smooth, but reanalysis of the same specimen revealed that it is actually sculptured by weak annulations and very fine transverse growth lines. Kobayashi (1934) emphasized that this species is closely similar to Sactorthoceras makkolense, except for the sig- moidal curvature of the conch. However, as Shimizu and Obata (1935a) pointed out, the sigmoidal mode of nautiloids from the Jigunsan Formation including Sigmocycloceras kogenense (Kobayashi), presumably originated by secondary deformation rather than from biological causes. Re-analy- sis of this specimen in longitudinal section indicates that over half of the right cameral portion is abraded and worn away and subsequently the chambers were filled with sedi- ment. Therefore, this specimen probably suffered some secondary deformation from one side. It seems likely that this force together with compactional load changed this specimen to a sigmoidal form. Thus, the original mor- phological features of the type specimen of Kobayashis Sigmorthoceras sigmoidale are identified with those of Sactorthoceras makkolense, indicating that the former species is a junior synonym of the latter. Meanwhile, Kobayashi (1934) established Kawasakiceras densistriatum on the basis of its characteristic annulated and striated ornamentation on the surface. In the holotype (UMUT PM634), the large-sized ventral endosiphuncle which is a primary morphologic feature for the endoceroid nautiloids such as Kotoceras can not be detected. Re- examination of the specimen strongly suggests that Kobaya- shi mistakenly interpreted the fracture line through the center as holochoanitic septal necks in his retouched figure in longitudinal section with a body chamber (Kobayashi, 1934, pl. 14, fig. 7; see also Figure 6). The right-half portion of the logitudinally sectioned type specimen may have been regarded as a ventral siphuncle. Also, the endocone which is the vacant space formed by the last endosheath is not observed in the portion that was considered by Kobayashi (1934) as the siphuncle. Therefore the septa are extended to the ventral margin and continue to the right-half portion. This fact is revealed not only by the preserved successive septa in longitudinal section but also by the camerae exposed on the lateral side of the specimen. In this way, this longitudinally sectioned specimen appears to represent a remaining part through which the siphuncle does not pass. Unfortunately, the other half is missing. It is evident that Kawasakiceras densistriatum does not possess a large ven- tral siphuncle as in the species of Kotoceras, but has a centrally located narrow siphuncle. In addition, the surface + Figure 5. Sactorthoceras makkolense (Kobayashi, 1927). ta, b. Partial phragmocone (KPE20036) from SN835, 1a: lateral view, <1, 1b: details of surface ornamentation, showing the annulations and fine growth lines, x5. 2a, b. Fragmen- tary phragmocone (KPE20032) from DJ500, 2a: longitudinal section, showing the siphuncle and septa, <1, 2b: septal view, venter down, showing the position of the siphuncle, x1. longitudinally polished section, 1. showing the phragmocone and subsequent body chamber, » section, showing the slightly inflated siphuncular segments, 1. nal section, showing the internal cameral structure, x1. 3. Naturally weathered phragmocone (KPE20030) from DJ500, 4. Incomplete large conch (KPE20033) from SN835, lateral view of partial conch, 5. Partial phragmocone (KPE20031) from DJ500, longitudinal 6. Partial phragmocone (KPE20037) from SN809, longitudi- Ordovician cephalopods from Korea 75 76 Cheol-Soo Yun Figure 6. “Kawasakiceras densistriatum Kobayashi”, UMUT PM634, which is here assigned to Sactorthoceras makkolense (Kobayashi). 1. Lateral view, *0.5. 2. Longitu- dinal section, x0.5. 3. Sketch based on Kobayashi's view, showing the broad ventral siphuncle. 4. Sketch based on reexamination of the holotype, showing the septa instead of siphuncle. Longitudinal (upper) and cross (lower) sections are shown in 3 and 4. ornamentation agrees well with the pattern of the species of Sactorthoceras. Accordingly, this species is attributed to Sactorthoceras makkolense (Kobayashi, 1927), based on the moderately concave septa, probably central narrow siphun- cle and annulated surface ornamentation with a fine trans- verse striation. Comparison.—This species is similar to Sactorthoceras wongiforme Kobayashi from the Jigunsan Formation of Maggol and Hwangjiri (Kobayashi, 1934, p. 410, pl. 20, fig. 10 ; pl. 31, figs. 1, 2) in its tubular siphuncle and moderately con- cave septa, but differs from the latter in its broader siphuncle and higher camera. Sactorthoceras tenuicurvatum Kobayashi from the Jigun- san Formation of Homyeong and Sanaegol (Kobayashi, 1934, p. 409, pl.16, figs.1,2; pl.17, figs.9,10) is readily distin- guished from this species by its gentle curvature and ellipti- cal section of the compressed conch. This species resembles Sactorthoceras sp. from the Ce- phalopod Shale at Hovindsholm, Helggya, Oslo region, Norway (Sweet, 1958, p. 60, pl. 3, fig. 12; pl. 4, figs. 1, 7), but its septal concavity is nearly three times of cameral height, while that of the latter species is less than half the length of a camera. Occurrence.—Rarely occurs at the localities SN802, SN809, SN835, and DJ500 in the Middle Ordovician Jigunsan Formation. Subclass Endoceratoidea Order Endocerida Family Endoceratidae Genus Kotoceras Kobayashi, 1934 Type species.—Kotoceras typicum Kobayashi, 1934 from the Jigunsan Formation of Maggol. Generic diagnosis.—Longiconic or somewhat curved ortho- ceracone, subcircular to ovate in cross section; siphuncle marginal, broad, nearly a half of the dosoventral conch diameter or less, in actual contact with slightly flattened ventral wall; endocones extending much farther forward ventrally than on dorsal side, apical end slightly closer to the dorsal side than the ventral one; septal necks holo- choanitic ; suture disconnected at ventral flattening ; sur- face smooth. Remarks.—Kotoceras is one of the Asiatic endemic genera from the Jigunsan Formation, Korea, and several species of the genus are known from China and Siberia. The diagnos- tic generic characters are the asymmetric endosiphocone and the disconnected septal suture on the ventral side. Kobayashi (1934) emphasized that Kotoceras is easily distin- guished from other related genera, Endoceras, Vaginoceras, and Cameroceras in having the marginal siphuncle in actual contact with the shell wall on the broadly flattened venter. Flower (1958) recognized that his Lamottoceras is very similar to the Asiatic Kotoceras, in which holochoanitic septal necks are present. However, the genus Lamottoceras differs from Kotoceras in having aneuchoanitic septal necks and thick connecting rings. Kotoceras grabaui (Kobayashi, 1927) Figures 3-3a, b; 7-1—4; 8-1—4 Vaginoceras grabaui Kobayashi, 1927, p. 79, pl. 18, figs. 1a-c, 2. Vaginoceras frechi Kobabyashi, 1927, p. 179, pl. 18, figs. 2a-c. Kotoceras grabaui (Kobayashi). Kobayashi, 1934, p. 395, pl. 11, figs. 5-8; pl. 12, fig. 6; pl. 14, figs. 5-8. Kotoceras frechi (Kobayashi). Kobayashi, 1934, p. 395 (not fig- ured). Type.—The best preserved and largest specimen (UMUT PM631) is designated here as the lectotype of Kotoceras grabaui (Kobayashi) (Figures 3-3a, b). Material.—Eleven specimens including the five figured ones (KPE20042, KPE20043, KPE20044, KPE20045, UMUT PM3). Specific diagnosis.—Subcircular to elliptical in cross sec- Ordovician cephalopods from Korea 77 Figure 7. Kotoceras grabaui (Kobayashi, 1927). 1a-c. Partial phragmocone (KPE20042) from SS663, <1, 1a: ventral view, showing the disconnected septal suture, 1b: dorsoventral section, venter on left, showing the large siphuncle with endosiphuncular deposits and closely spaced septa, 1c: lateral view, venter on left side, showing the transverse septal suture. 2. Strongly compressed phragmocone (KPE20043) from MG350, dorsolateral view, venter on right, showing the septal neck impressions on ventral side of the siphuncle, x1. Sa, b. Partial phragmocone (KPE20044) from MG357, x1, 3a: ventral view, showing the siphuncle-septal neck portion, 3b: apical view of septum and siphuncle, showing the nearly circular conch cross section and slightly depressed siphuncle. 4. Partial phragmocone (KPE20045) from MG357, ventral view, showing the somewhat flattened ventral side, <1. tion ; septal suture transverse, but gradually bends adapical- Description.—Conch medium-sized longiconic orthocera- ly and then turns into longitudinal section; septal impres- cone, represented by several fragmentary phragmocones, its sions sloping from venter to dorsal; siphuncle large, nearly diameter gently enlarging at a rate of 1 mm per conch length half or a little less than half the dorsoventral conch diameter ; of 9mm in KPE20045 (Figure 7-4); conch elliptically ovate camerae crowded. to subcircular in cross section, slightly dorsoventrally 78 Cheol-Soo Yun Figure 8. which is here assigned to Kotoceras grabaui (Kobayashi). 1. “Kotoceras frechi (Kobayashi)’, UMUT PM3, Longitudinal section shown by an acetate peel, X2. 2. Cross section by the same method, x2. 3,4. Sketches of longitudinal section and cross section, respectively, showing the strongly depressed cameral portion and broken septa. Arrows indicate the direction of compaction. depressed, ratio of the dorsoventral to lateral diameter of the conch near the adoral portion being 7:8 in KPE20042 (Figure 7-1); siphuncle marginal, in actual contact with the ventral wall, its cross section elliptical to subcircular, ventrally more flattened, expansion rate of the siphuncle commensu- rate with that of the conch; septal impression on the si- phuncle running obliquely down from ventral to dorsal, its distance being about 2 mm or more in KPE20043 (Figure 7- 2); Camerae crowded, averaging 11 in the distance of the dorsoventral diameter of the conch, tending to broaden adorally in the middle part of the phragmocone, but finally attaining a height of 1.5 mm in KPE20042 (Figure 7-1); septal necks holochoanitic ; septa moderately concave adorally, their depth corresponding to one and a half times the cameral height, increasing adorally where attaining a little more than twice the cameral height; septal ridge on the siphuncle running obliquely from ventral to dorsal; septal suture laterally transverse, but dorsally abruptly inclined backward, gradually bending posteriorly on the ventral side, and then becoming parallel to vertical axis ; no endocone observed; camera filled with clastic sediments; surface apparently smooth. Remarks.—Kobayashi (1927) proposed Vaginoceras frechi from the Jigunsan Formation of Maggol, based on a single specimen (p.179, pl. 18, figs. 2a-c; UMUT PMS; Figure 8). Kobayashi (1934) subsequently reassigned this species to Kotoceras. According to his description, the characteristics of this species are summarized as follows: “The septum is gently inclined near the siphuncle but very steeply near the shell wall and is subangulated at a point where the septum bends from a gentle to a sharp angle”. Kobayashi (1934) mentioned that this species is distinguished from Kotoceras typicum by having a more rapidly expanded conch, broader siphuncle and more concave septa. However, the monotype of this species, UMUT PMB, is secondarily deformed along the dorsal margin, so that the above features may not fairly represent the specific diagno- sis (Figure 8). Firstly, in the longitudinal section, septa of the dorsal portion are crushed by depression and then three or four septa are duplicated so as to be obliquely parallel with the shell wall. Most of the septa on the dorsal margin are irregularly arranged and broken. Because the clusters of broken septa are piled up longitudinally along the dorsal wall, the degree of convexity of each septum appears to change abruptly at a point midway on the septa. Secondly, the siphuncle has an unusually large diameter as compared with the conch diameter. In every species of Kotoceras, the siphuncle generally takes up one-third to a half of the conch diameter. The cameral portion in Kotoceras frechi is only one-third. The appearance must have been deformed by the effect suffered from sediments outside the dorsal portion. Thus, the diagnostic features of the specimen described as Kotoceras frechi by Kobayashi (1927, 1934) may be the result of diagenetic deformation, and therefore this taxon can be reassigned as a junior synonym of Kotoceras grabaui (Kobayashi, 1927). In the meantime, Chen and Zou (1984, p. 80, pl. 16, fig. 6) identified a longitudinally sectioned specimen from the Lower Ordovician Yaoxian Formation of Shaanxi, North China as Kotoceras frechi. However, this specimen is assignable to Kotoceras multiseptum Kobayashi from the Jigunsan Formation of Maggol in having crowded and deeply con- caved septa and a broad siphuncle. Comparison.—This species is comparable to Kotoceras stolbovense Balashov from the Middle Ordovician Krivoluts- ky Formation of the Siberian Platform (Balashov, 1962, p. 32, pl. 26, figs. 1a-d) ; however, the present species has a much shallower septal concavity and slightly larger siphuncle. Kotoceras typicum Kobayashi from the Jigunsan Formation of Maggol (Kobayashi, 1934, p. 392, pl. 11, figs. 1-4) is distin- guished from K. grabaui by its more broadly spaced septa, nearly circular cross section of the conch in juvenile shell, Ordovician cephalopods from Korea 79 and shell surface with fine growth lines. In the septal distance and the shape of the cross section, Kotoceras multiseptum Kobayashi from the Jigunsan Forma- tion of Maggol (Kobayashi, 1934, p. 394, pl. 12, figs. 1,2; pl. 13, figs.1-3) is closely allied to K. grabaui, but its conch expansion rate is much more rapid than that of the latter. Kotoceras cylindricum Kobayashi from the Jigunsan Forma- tions of Maggol and Homyeong (Kobayashi, 1934, p. 393, pl. 12, figs. 7-9; pl. 18, figs. 8, 9) is easily distinguished from K. grabaui by its circular cross section with a depressed siphun- cle and more crowded septa. Occurrence.—Middle Ordovician Jigunsan Formation, localities ; SR900, SS663, MG343, MG350 and MG357. Acknowledgments | express my thanks to Kazushige Tanabe (University of Tokyo) for his critical reading of the manuscript and valuable suggestions. | am grateful to Takeo Ichikawa (Tokyo Univer- sity Museum) for access to the late Prof. Kobayashi’s collec- tions under his care. | am indebted to Seong-Young Yang (Kyungpook National University) in Korea for his kind advice and encouragement. Thanks are also extended to Yasunari Shigeta and Shin'ichi Sato (both National Science Museum) for their kind assistance in the field and providing specimens. Special thanks are due to to Royal H. Mapes (Ohio University) for his thoughtful review and going over the language of the present paper. References cited Balashov, Z. G., 1962: Ordovician nautiloids of the Siberia Platform. 131p, 52pls. Leningrad University Press, Leningrad. (in Russian) Boll, E., 1857: Beitrage zur Kenntniss des silurischen Ce- phalopoden im norddeutschen Diluvium und den anste- henden Lagern Schwedens. 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Paleontological Research, vol. 3, no. 2, pp. 81-87, 2 Figs., June 30, 1999 © by the Palaeontological Society of Japan Esgueiria futabensis sp. nov., a new angiosperm flower from the Upper Cretaceous (lower Coniacian) of northeastern Honshu, Japan MASAMICHI TAKAHASHI’, PETER R. CRANE’ and HISAO ANDO* ‘Department of Bioscience, Kagawa University, Takamatsu, 760-8522, Japan "Department of Geology, The Field Museum, Chicago, Illinois, 60605-2496, U.S.A. “Department of Environmental Sciences, Faculty of Science, Ibaraki University, Mito 310-8512, Japan Received 12 December 1998, Revised manuscript accepted 12 March 1999 Abstract. Bulk sieving of samples from the Ashizawa Formation, Futaba Group (lower Coniacian) of northeastern Honshu, Japan, has yielded a well-preserved plant mesofossil assemblage comparable to those recently described from eastern North America, Europe and central Asia. The most distinctive component of the assemblage is a new species of the genus Esgueiria (Esgueiria futabensis sp. nov.), a fossil flower known previously only from the Upper Cretaceous (Campanian-Maastrichtian) of Portugal. A possible additional species of the genus has also been recovered from a second mesofossil assemblage in the Tamayama Formation (lower Santonian). The occurrence of Esgueiria in Europe and eastern Asia during the Late Cretaceous indicates that despite the vegetational differences between these areas inferred from fossil pollen, some elements were widespread across middle paleolatitudes, presaging the strong floristic similarities among mid- and high latitude regions of the Northern Hemisphere during the early Tertiary. Key words: Angiosperm flower, Ashizawa Formation, Coniacian, Esgueiria futabensis sp. nov., Santonian, Tamayama Formation Introduction Studies of the early fossil history of flowering plants (an- giosperms) have been revolutionized over the last 15 years by the discovery of abundant, small, well-preserved and sys- tematically informative fossil flowers in assemblages of Cretaceous plant mesofossils from Europe and eastern North America (e.g., Friis and Skarby, 1982 ; Friis, 1983 ; Knobloch and Mai, 1984 ; Friis et al., 1994 ; Crane et al., 1994). These specimens have yielded important information relating to the early diversification of many lineages of extant angiosperms and the evolution of their pollination and dispersal biology (eg. Crane et al, 1995). Only recently have similar mesofossil assemblages been recognized in central Asia (Frumina et al., 1995, Frumin and Friis, 1996, 1999), and we now report that they also occur in eastern Asia. In this paper we describe the most characteristic of several fossil flowers in newly discovered plant mesofossil assemblages from the Futaba Group (lower Coniacian-lower Santonian) of Northeast Japan. Materials and methods Plant fossils were isolated from two sets of bulk samples collected at two different levels in the Futaba Group exposed in Fukushima Prefecture, northeastern Honshu, Japan. The fossils are small, three-dimensional and charcoalified or lignitized mesofossils. The Kamikitaba plant mesofossil asssemblage (sample F16) was isolated from a poorly sorted, carbonaceous, black, sandy siltstone collected along a tributary of the Kitaba River in Kamikitaba, Hirono-machi (Study Route B of Ando et al. 1995; 3712’N, 140°57’E). These samples were from the Asamigawa Member of the Ashizawa Formation, which is interpreted as alluvial fan sediments (Ando, 1997). The Kohisa plant mesofossil assemblage (sample F11), comprised a poorly sorted, beige, sandy siltstone with scattered carbonaceous flecks. It was collected along the Kohisa River, Kohisa, Ouhisa-machi northeast of Iwaki City (Study Route N of Ando et al., 1995 ; 37 10'N, 140°57’E). These samples were from the middle part of the Tamayama Formation, which is interpreted as braided river flood plain sediments with lagoonal facies in the uppermost part (Ando, 1997). The Futaba Group comprises fluvial to shallow marine 82 Masamichi Takahashi et al. sediments in the southern Abukuma Belt of Northeast Japan (Ando et al., 1995). The Ashizawa Formation is the lower- most formation in the Futaba Group, and is overlain by the Kasamatsu Formation, which itself is overlain by the Tamayama Formation. Based on the occurrence of lower Coniacian ammonites and inoceramids in the middle of the Ashizama Formation, and a lower Santonian inoceramid (Inoceramus amakusensis) in the upper part of the Tamayama Formation, the Futaba Group is thought to range in age from early Coniacian to early Santonian. The age of the plant- bearing sediments in the Asamigawa Member is probably early Coniacian (ca. 89 million years before present; Grad- stein et al., 1995), whereas the age of the plant-bearing sediments in the Tamayama Formation is probably early Santonian (ca. 85 million years before present; Gradstein et al., 1995). Bulk samples of ca. 500 kg of carbonaceous, black, poorly sorted sandy siltstone were dried in the laboratory, disag- gregated in water and sieved through a 0.8mm mesh. Recovered carbonaceous debris was then cleaned in hydro- fluoric and hydrochloric acids, thoroughly rinsed in water, and dried in air. Individual specimens selected for scanning electron micrsocopy were mounted on scanning electron microscope stubs, sputter coated with platinum-palladium and examined in a Hitachi S-800 field emission scanning electron microscope. All specimens are deposited in the paleobotanical collections of the Field Museum of Natural History, Chicago (PP). Systematic description Class Magnoliopsida (angiosperms) Genus Esgueiria Friis, Pedersen and Crane, 1992 The genus was established by Friis, Pedersen and Crane (1992) based on material from two localities of Campanian- Maastrichtian age in the northern part of the Western Portuguese Basin, Beira Litoral, Portugal. Two species were distinguished : Esgueiria adenocarpa from the Esgueira locality (the type species), and Esgueiria miraensis from the Mira locality. Esgueiria futabensis sp. nov. Figures 1-1—1-8, 2-1, 2-2, 2-4, 2-5 Material— PP45389 (holotype). 45390-PP45417. Type Locality and Horizon.—Kamikitaba plant mesofossil assemblage (sample F16), along a tributary of the Kitaba River in Kamikitaba, Hirono-machi, (Study Route B of Ando et al. 1995; 37°12’N, 140°57’E). Etymology.—Named after the Futaba Group, the geologi- cal unit from which the specimens were recovered. Specific Diagnosis.—Ovary and fruit narrowly elongate, rounded at the base. Peltate (glandular) trichomes on the base of the styles, and also in rows, often of ten or more, on the hypanthium. Simple trichomes densely spaced on the surface of the ovary, calyx and styles. Prominent recep- tacular mounds present between the stamens and the perianth. Dimensions.—All specimens lacking a well-preserved corolla: length of ovary: (1.85-) 2.76 (—3.3) mm; breadth of ovary: (0.7—) 1.12 (—1.5)mm; length of sepals: unknown; breadth of sepals: (0.3-) 3.62 (—0.4)mm: 25 specimens measured. Pollen not identified. Description and Remarks.—The species is known from 29 complete or fragmentary flowers from the Kamikitaba assemblage preserved mainly as charcoalified specimens. Similar material from the Kohisa assemblage is not referred to E. futabensis, and probably represents a different species of Esgueiria (see below). Many of the specimens are broken or abraded fragments of the inferior ovary, but almost all show either the distinctive peltate glands, or the remains of the glands and their secretion in one or more longitudinal grooves in the ovary wall. None of the specimens is a bud and most of the material probably represents mature fruits with a partially persistent perianth and androecium. None of the specimens has yielded information on inflorescence structure, anthers, pollen or ovules. Flower : Flowers are epigynous (Figure 1-1) and the calyx is visible in most specimens. Remains of filament and styles bases are also commonly preserved. Unequivocal remains of the petals are rarely present. None of the specimens have a pedicel or prophyll preserved. Perianth : The calyx consists of five free sepals (Figure 1- 2). In all specimens the calyx lobes are broken and their shape cannot be established reliably (Figures 1-2, 1-6, 2-5). Other specimens ; PP > Figurei. Esgueiria futabensis sp. nov., Kamikitaba assemblage, Asamigawa Member, Ashizawa Formation (lower Coniacian), Futaba Group, Fukushima Prefecture, northeastern Honshu, Japan. 1. Holotype, lateral view of well-preserved epigynous flower showing peltate and simple trichomes on the ovary wall, note remains of sepals and three styles at flower apex, as well as the protruding hemispherical glands in the outer tissues of the ovary wall, PP45389, x35. 2. Holotype, apex of flower showing sepals, possible remains of corolla, receptacular mounds, stamen filaments and three styles, PP45389, “73. 3. Holotype, detail of small, peltate, trichome from base of style, note also thick wall of broken trichome, PP45389, 930. 4. Lateral view of abraded specimen showing ovary with longitudinal ribs denuded of trichomes, note remains of sepals and stout style base at the apex of the flower, PP45403, «35. 5. Holotype, detail of peltate and simple trichomes from ovary wall, note also the opening of a hemispherical gland in the ovary wall, PP45389, «100. 6. Detail of apical portion of specimen in Figure 1-4 showing sepals, receptacular mounds, filament bases and stout base of style, PP45403, x72. 7. Holotype, detail of simple trichome from ovary wall, note verrucate surface, PP45389, «920. 8. Detail of apex of flower in Figure 1-4 showing remains of sepals, ten prominent receptacular mounds, eight (possibly nine) filament bases and stout base of style, PP45403, x 72. Cretaceous angiosperm flower Masamichi Takahashi et a/. Figure 2. Esgueiria futabenis sp. nov. and Esgueiria sp., Futaba Group, Fukushima Prefecture, northeastern Honshu, Japan. 1, 2, 4,5, Esgueiria futabensis sp. nov., Kamikitaba assemblage, Asamigawa Member, Ashizawa Formation (lower Coniacian). 3,6, Esgueiria sp., Kohisa assemblage, middle part of the Tamayama Formation (lower Santonian). 1. Lateral view of abraded specimen showing numerous peltate trichomes in two grooves in the ovary wall, PP45391, x32. 2. Lateral view of abraded specimen showing remains of peltate trichomes in two grooves in the ovary wall, note remains of sepals and stout base of style at the floral apex, PP45393, «30. 3. Lateral view of compressed specimen showing three prominent peltate trichomes on the ovary wall, note that the peltate trichomes are larger and fewer than in E. futabensis, PP45419, «17. 4. Detail of specimen in Figure 2-1 showing remains of peltate trichomes and unabraded portion of ovary wall, PP45391, «90. 5. Apex of specimen in Figure 2-2 showing sepals, bases of two filaments and stout base of style, PP45393, «67. 6. Apex of specimen in Figure 2-3 showing stamen filament surrounding stout base of style, note remains of receptacular mounds between the sepals and stamen bases, PP45419, x 27. Cretaceous angiosperm flower 85 However, there are sufficient specimens in which parts of the calyx are preserved to infer that it was persistent through fruit development. The corolla is not clearly visible in any of the specimens, although a few show fragments of tissue that may represent the bases of petals. The rare presence of the corolla in more than 1,000 specimens of E. adenocarpa led to the conclusion that the corolla was probably caducous (Friis et a/., 1992), and this may also have been the case in E. futabensis. Receptacular mounds : Most specimens show prominent, more or less ellipsoidal mounds of tissue, ca. 0.2 mm broad and ca. 0.1mm deep, on the receptacle between the filament bases and the calyx (Figures 1-6, 1-8). In one specimen there are ten mounds that alternate with the stamen bases (Figure 1-8). The nature of these mounds is uncertain, but judging from their position and swollen structure (Figures 1-2, 1-6) it is possible that they are nectary lobes. A possible nectary was observed in E. adenocarpa, but in the more usual postion for a disc nectary, between the stamens and the style bases (Friis et al., 1992). In E. futabensis it is clear that the receptacular mounds are outside the androecium between the sepals and the stamens (Figure 1-8). Androecium: None of the specimens has a complete stamen preserved and we have been unable to detect pollen on any of the flowers. However, the position of the stamen filaments indicates stamens were both opposite to, and alternate with, the sepals (Figure 1-8). Based on this pattern an androecium of ten stamens would be inferred. However, the best preserved androecium (Figure 1-8) shows the remains of only eight (or possibly nine) filaments. It is uncertain whether this indicates incomplete preservation, or whether less than ten stamens developed as in E. adenocar- pa (Friis et al., 1992). There is no clear indication that stamens were arranged in more than one whorl (Figure 1-8). Gynoecium: The ovary is inferior and unilocular. The holotype clearly shows that there were three free styles, at least distally (Figure 1-2). Proximally, however the styles appear to have been fused into a single, stout, style base (Figures 1-6, 2-5). The ovary is narrowly elongated, more or less parallel-sided and with a rounded base (Figures 1-1, 1-4, 2-1,2-2). The ovary wall is pleated into five longitudinal grooves that alternate with sepals, and five longitudinal ridges that are on the same radius as the sepals. The ovary wall is about 0.05 mm thick. In several specimens there are protruding hemispherical glands, ca. 0.1mm in diameter, in the outer tissues of the ovary wall. In abraded specimens that lack the epidermis the inner layers of the ovary wall are seen to be composed of small equiaxial sclerenchyma cells ca. 0.01 mm in diameter. Lining the locule there is a inner epidermis of larger cuboidal cells. Trichomes: Two different types of trichomes have been Observed on the specimens. They are best developed and most easily Observed on the surface of the ovary but also occur on the stout style base. Simple trichomes: Simple hairs are scattered all over the Ovary and other floral organs. The hairs may be up to ca. 0.2 mm long, are more or less parallel-sided for much of their length, and appear to be unicellular (Figure1-7). At the apex they have an acute point. Broken specimens show that the trichomes are thick-walled (Figure 1-3). The tri- chome wall close to the point of attachment seems to be thinner and somewhat collapsed (Figure 1-7). In well- preserved specimens the trichome wall is ornamented with distinctive elongated verrucae (Figures 1-3, 1-7). Peltate trichomes: Peltate trichomes (inferred to have been glandular) are arranged in a single row in the grooves in the ovary wall (Figures 1-5, 2-4). The peltate trichomes never occur side-by-side. Smaller peltate trichomes also occur on the style bases (Figure 1-3). On the ovary wall the peltate trichomes are typically more or less circular, 0.12-0.18 mm in diameter, and appear to consist of a central stalk and a shieldlike head. A clear radiating structure among the cells comprising the head has not been seen. The number of peltate trichomes in a single row varies, but it is often between 10 and 20 (Figure 1-1, 2-1). Frequently, under the light microscope, the peltate trichomes appear to be embed- ded in a black shiny substance, which is often present even when the trichomes themselves are not clearly visible (Figure 2-2). We infer that this represents the remains of a secre- tion associated with the glandular trichomes. Peltate tri- chomes also occur on the style-bases of well-preserved specimens scattered among the simple hairs. These tri- chomes are generally smaller (ca. 0.06 mm in diameter) and less prominent than those on the ovary wall but are similar in structure (Figure 1-3). Comparison Esgueiria futabensis clearly shows the diagnostic features of the genus (Friis et al. 1992). The flowers are small, epigynous and bisexual with the perianth and androecium organized on a basically pentamerous plan. There is a Calyx of five free sepals and an androecium with more than five stamens. The ovary is unilocular with three styles. The indumentum consists of simple stiff hairs and the characteristic multicellular, peltate trichomes. Esgueiria futabensis is clearly distinguished from the two other species of the genus. It differs from the type species, E. adenocarpa, in being generally larger : (1.85-) 2.76 (—3.3) mm rather than (1.5-) 1.88 (2.2) mm long. The shape of the ovary is also more or less parallel-sided, rather than obovate, and the base of the ovary is rounded rather than pointed (compare Figures 1-1, 1-4, 2-1, 2-2 with Friis, Pedersen and Crane, 1992, Plate1). The peltate trichomes are smaller (0.12-0.18 mm in diameter) in E. futabensis than in E. adenocarpa (0.2-0.3 mm in diameter). Also significant is the number of peltate glands in a single groove on the ovary wall, which is often 10-20 in E. futabensis, compared with a maximum of five or six in E. adenocarpa. The occurrence of peltate glands on the style bases (Figure 1-3) is a further difference between E. futabensis and E. adenocarpa, but a similarity with E. miraensis. However, compared to E. miraensis, E. futabensis is larger: length of ovary (1.85-) 2.76 (—3.3)mm compared to 0.8-0.95 mm. The ovary of E. futabensis is also long and narrow, rather than campanulate as in E. miraensis. Other Esguieria flowers are known from the Kohisa plant mesofossil assemblage, which is younger (early Santonian) 86 Masamichi Takahashi et a/. than the Kamikitaba assemblage that yielded E. futabensis. However, the Kohisa specimens are larger than those from Kamikitaba (length of ovary [2.75-] 3.5 [—4] mm), are more obovate in shape with a more pointed base, and also have significantly larger peltate trichomes (Figures 2-3, 2-6). These specimens may represent a fourth species of Esgueir- ia, but because only eight specimens are known (PP45418- PP45425), they are here left unassigned as Esgueiria sp. Discussion In terms of systematic affinities, E. futabensis does not add to previous discussions of a relationship between Esgueiria and the extant angiosperm family Combretaceae. .. However, this new species is important in several respects. It docu- ments the occurrence of mesofossil assemblages with well- preserved angiosperm flowers in the Upper Cretaceous of Japan that are comparable in their quality of preservation to those recently described from eastern North America, Europe and central Asia. It adds a new species to the very small number of fossil angiosperm reproductive structures so far described from the Upper Cretaceous of Japan (Stopes and Fujii, 1910; Ohana and Kimura, 1987 ; Nishida, 1985, 1991, 1994 ; Nishida and Nishida 1988; Nishida et a/., 1996). It also provides the first evidence of botanically informative plant fossil assemblages (other than palynofloras ; Miki, 1977 ; Takahashi, 1988) in the Futaba Group. The discovery of Esgueiria futabensis also has interesting biogeographic implications and extends substantially the range of a genus previously known only from the Campanian-Maastrichtian of Portugal. Based on pollen and spore assemblages Portugal was part of the Nor- mapolles Province during the Late Cretaceous. Japan is generally included in the Aquilapollenites Province (Hern- green et al., 1996) based on the first appearance of tripro- jectate grains in Late Cretaceous sediments younger than those of the Futaba Group (Miki, 1977). The occurrence of Esgueiria in both eastern Asia and southern Europe docu- ments that some Late Cretaceous floristic elements had very broad geographic distributions, presaging the strong floristic similarities evident at middle and high latitudes of the Northern Hemisphere during the early Tertiary. Acknowledgments This work was supported by Grant-in-Aids (08640891 and 09640827) from the Ministry of Education, Science, Sports and Culture of Japan to MT., and by fellowships from the Japan Society for the Promotion of Science in 1997 (S-97128) and 1998 (S-98106) to PRC. This work was also supported in part by U.S. National Science Foundation Grant EAR- 9614672 to PRC. PRC is also grateful to Kagawa University for its hospitality during completion of this research. References cited Ando, H., Seishi, M., Oshima, M. and Matsumaru, T., 1995: Fluvial-shallow marine depositional systems of the Futaba Group (Upper Cretaceous): Depositional facies and sequences. Journal of Geography, vol.104, p. 284-303. (in Japanese) Ando, H., 1997: Apparent stacking patterns of depositional sequences in the Upper Cretaceous shallow-marine to fluvial successions, northeast Japan. Memoirs of the Geological Society of Japan, vol. 48, p. 43-59. Crane, P. R., Friis, E. M. and Pedersen, K. 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Philosophical Transactions of the Royal Society, B, vol. 201, p. 1-90. Takahashi, K., 1988: Palynology of the Upper Cretaceous Futaba Group. Bulletin of the Faculty of Liberal Arts, Nagasaki University (Natural Science), vol. 28, p. 67-183. Paleontological Research, vol. 3, no. 2, pp. 88-94, 3 Figs., June 30, 1999 © by the Palaeontological Society of Japan Boreal-type brachiopod Yakovlevia from the Middle Permian of Japan JUN-ICHI TAZAWA Department of Geology, Faculty of Science, Niigata University, Niigata, 950-2181, Japan Received 15 April 1998 ; Revised manuscript accepted 25 March 1999 Abstract. The following three species of the Boreal-type brachiopod genus Yakovlevia are described from the Middle Permian (Kungurian to Ufimian) of the Hida Gaien (=Hida Marginal) and South Kitakami Belts, Japan: Y. kaluzinensis Fredericks, Y. mammata (Keyserling) and Y. mammatiformis (Fredericks). The occurrence of Yakovlevia together with various Boreal- and Tethyan-type brachiopods in the Middle Permian of the two belts suggests that these regions were probably a continental shelf at the eastern margin of the Sino-Korean block in Middle Permian time. Key words: Boreal-type brachiopod, Hida Gaien Belt, Middle Permian, Sino-Korean block, South Kitakami Belt, Yakovlevia Introduction Brachiopods are important and useful for Permian global palaeobiogeography as the predominant element in the benthic fauna at that time (Stehli, 1973; Waterhouse and Bonham-Carter, 1975 ; Grunt, 1995 ; Shi et al., 1995 ; Jin and Shang, 1997). Yakovlevia is a typical Boreal-type, Middle Carboniferous to Middle Permian productoid genus belong- ing to the family Yakovleviidae Waterhouse, 1975. This genus was established by Fredericks in 1925, with Chonetes (Yakovlevia) kaluzinensis Fredericks, 1925 from the Middle Permian Chandalaz Formation of Cape Kalouzin in the Vladivostok area, South Primorye as the type species. The morphology and classification of Yakovlevia and related genera have been fully discussed by Licharew (1947), Muir- Wood and Cooper (1960), Kotljar (1961), Muir-Wood (1965), Cooper and Grant (1975), Waterhouse (1975), and Shi (1995). Concerning the relationship of Yakovlevia with Muirwoodia Licharew, 1947, | follow Kotljar (1961), Cooper and Grant (1975), and Shi (1995), all of whom considered Muirwoodia as a junior synonym of Yakovlevia. The purpose of this paper is to describe three Yakovlevia species, Y.kaluzinensis Fredericks, 1925, Y. mammata (Keyserling, 1846), and Y. mammatiformis (Fredericks, 1926), from the Middle Permian (Kungurian to Ufimian) of the Hida Gaien and South Kitakami Belts, Japan, discussing their palaeobiogeographical significance. The material utilized is: eight specimens of Y. kaluzinensis from the lower part of the Moribu Formation in the Moribu area, Hida Mountains (Hida Gaien Belt), central Japan; two specimens of Y. mammata from the lower Kanokura Formation in the Kesen- numa area, southern Kitakami Mountains (South Kitakami Belt), northeast Japan; and the single specimen of Y. mammatiformis from the upper Iriishikura Formation in the Takakurayama area, Abukuma Mountains (South Kitakami Belt), northeast Japan (Figure1). These specimens are housed in the Department of Geology, Faculty of Science, Niigata University, Niigata (NU-B) and the Institute of Geology and Palaeontology, Tohoku University, Sendai (IGPS). Palaeobiogeographical significance of Yakovlevia Recently Shi (1995) summarized the stratigraphical and geographical distribution of Yakovlevia using 45 species of this genus. According to him, the genus is distributed from the Middle Carboniferous to Middle Permian of the Boreal Realm and the transitional zone between the Boreal and Tethyan Realms, namely, the Northern Transitional Zone (Sino-Mongolian Province) and the Cordilleran Province (see Shi, 1995, figs. 2, 8, table 1). The former transitional zone is almost equal to the Inner Mongolian-Japanese Transition Zone of Tazawa (1991). As shown in Figure 2, the three Yakovlevia species de- scribed below clearly indicate a Boreal distribution. Y. kaluzinensis has been known from the Middle Permian (Kungurian to Ufimian) of South Primorye, eastern Russia, and the Hida Mountains, central Japan (Fredericks, 1925 ; Muir-Wood and Cooper, 1960; Kotljar, 1961 ; Licharew and Kotljar, 1978; Horikoshi et al. 1987; Tazawa, 1987). Y. mammata has been known from the Lower Permian (Artins- kian) to Middle Permian (Guadalupian) of Spitsbergen ; Timan and Pechora, northern Russia; Upper Yukon River, Yukon Territory; Grinnell Peninsula, Devon Island, Arctic Canada; Tien Shan, West China; Ekenalsileng, Jisu (Zhesi), Dong Ujimgin, Xi Ujimgin and Horgin Youyi Qiangi, Inner Mongolia, North China; South Primorye, eastern Russia ; Yakovlevia from Japan 89 138° KESENNUMA KAKURAYAMA Pacific Ocean Figure1. Map showing the fossil localities. southern Kitakami Mountains, northeast Japan (Keyserling, 1846 ; Koninck, 1847 ; Tschernyschew, 1902 ; Keidel, 1906 ; Chao, 1927; Grabau, 1931; Stepanov, 1937 ; Muir-Wood and Cooper, 1960; Harker in Harker and Thorsteinsson, 1960 ; Kotljar, 1961; Gobbett, 1963; Brabb and Grant, 1971; fanova, 1972 ; Lee and Gu, 1976; Licharew and Kotljar, 1978; Lee and Gu in Lee et a/., 1980 ; Liu and Waterhouse, 1985; Tazawa, 1987; Malkowski, 1988; Zhang, 1990; Nakamura et al., 1992 ; Kalashnikov, 1993). Y. mammatifor- mis is distributed in the Lower Permian (Sakmarian) to Middle Permian (Kungurian) of the northern Urals, Timan, Pechora Basin and Novaya Zemlya, northern Russia ; Omolon Massif, northeastern Russia ; South Primorye, eastern Russia ; Abu- kuma Mountains, northeast Japan (Fredericks, 1926 ; Kotljar, 1961 ; Mironova, 1964; Yanagisawa, 1967 ; Zavodowsky and Stepanov in Zavodowsky et al. 1970; Ifanova, 1972; Kulikov, 1974 ; Kalashnikov, 1983, 1993). The Middle Permian brachiopod faunas of the Hida Gaien and South Kitakami Belts are characterized by a mixture of Boreal and Tethyan elements, e.g., Yakovlevia, Cancrinella, Waagenoconcha, Megousia, Stenoscisma, and Spiriferella as the Boreal-type genera, and Leptodus, Enteletes, Transen- natia, Permundaria, and Urushtenoidea as Tethyan-type genera (Tazawa, 1987, 1991,1992; Nakamura and Tazawa, 1990), and closely resemble those of South Primorye, North- east China and Inner Mongolia (Tazawa, 1987, 1991, 1992). The occurrence of Yakovlevia together with various Boreal- and Tethyan-type brachiopods in the Middle Permian of the Hida Gaien and South Kitakami Belts supports the opinion of Tazawa (1991,1992), who considered that 1) the above regions belonged to the Southern Subzone of the Inner Mongolian-Japanese Transition Zone, and that 2) this sub- zone was being probably a piece of continental shelf border- ing the eastern margin of the Sino-Korean block, which was situated at a middle northern palaeolatitude in Middle Per- mian time (Figure 2). Systematic descriptions Order Productida Waagen, 1883 Suborder Productidina Waagen, 1883 Superfamily Linoproductoidea Stehli, 1954 Family Yakovleviidae Waterhouse, 1975 Genus Yakovlevia Fredericks, 1925 Type species— Chonetes (Yakovlevia) kaluzinensis Fredericks, 1925. 90 Jun-ichi Tazawa RES © Y. kaluzinensis A Y. mammata A Y. mammatiformis Inner Mongolian-Japanese Transition Zone Figure 2. Geographical distribution of Yakovlevia kaluzinensis Fredericks, Yakovlevia mammata (Keyserling) and Yakovlevia mammatiformis (Fredericks) in Middle Permian. (Palaeogeographic map after Ziegler et al., 1996). 1. Yukon Territory, 2. Devon Island, 3. Spitsbergen, 4. Omolon Massif, 5. Novaya Zemlya, 6. Pechora Basin, 7. Timan, 8. northern Urals, 9. Tien Shan, 10. Inner Mongolia, 11. South Primorye, 12. Moribu, Hida Mountains, 13. Kesennuma, southern Kitakami Mountains, 14. Takakurayama, Abukuma Mountains. AF: Africa, AN: Antar- ctica, AR: Arabia, AU: Australia, E: Eurasia, G: Greenland, IC: Indochina, IN: India, L: Lhasa, M: Mongolia, NA: North America, Q: Qangtang, SA: South America, SI: Sibumasu, SK: Sino-Korea, T: Tarim, Y : Yangtze. Yakovlevia kaluzinensis Fredericks, 1925 Figures 3-7—15 Chonetes (Yakovlevia) kaluzinensis Fredericks, 1925, p. 7, pl. 2, figs. 64-66. Yakovlevia kaluzinensis Fredericks. Muir-Wood and Cooper, 1960, pl. 133, figs. 5,6; Kotljar, 1961, text-figs. 1-3; Licha- rew and Kotljar, 1978, pl. 14, figs. 1, 2. Yakovlevia sp. Horikoshi et a/., 1987, text-figs. 3A, B; Tazawa, 1987, text-fig. 1.7. Material.—Eight specimens, from the lower Moribu Forma- tion in the Moribu area, Hida Mountains (Hida Gaien Belt), central Japan: (1) external and internal moulds of a pedicle valve, NU-B157 ; (2) internal moulds of three pedicle valves, NU-B158-160 ; (3) external and internal moulds of two bra- chial valves, NU-B161, 162; (4) external moulds of two brachial valves, NU-B163, 164. Description.—Shell large for genus, transversely sub- rectangular in outline, with greatest width at hinge line; length about 37 mm, width about 44mm in the smaller pedicle valve specimen (NU-B157); length 38mm, width about 60 mm in the largest and best preserved brachial valve specimen (NU-B163). Pedicle valve gently convex on venter, strongly genicu- lated, and followed by a long trail. Umbo small. Ears large, prominent, but not clearly differentiated from visceral part. Sulcus narrow and shallow, originating near umbo, and extending to anterior margin. External ornament of pedicle valve invisible except for a row of oblique spines just anterior to the posterior margin. Brachial valve nearly flat on vis- ceral disc, strongly geniculated, and followed by a short trail. Fold narrow and low on anterior half of valve. External surface of brachial valve ornamented by numerous fine costellae and several weak, irregular concentric rugae on visceral disc, costellae only on trail; costellae often bifurcat- ing and intercalating, numbering 11-13 costellae in 5mm at midvalve. Pedicle valve interior with a pair of small, elongate subtrigonal adductor scars and two large diductor scars. Diductor scars striated anteriorly and encircled by a strong ridge posterolaterally. Internal structure of brachial valve obscure in the present material. Comparison.—The Moribu specimens are referred to Yakovlevia kaluzinensis Fredericks, 1925, originally described by Fredericks (1925) from the Middle Permian in size and shape of the shells, especially in the transversely subrectan- gular outline. Yakovlevia impressa (Toula, 1875, p. 236, pl. 5, figs. 1a-c) from the Middle Permian of Spitsbergen differs from Y. kaluzinensis in having larger and more prominent ears. Yakovlevia mammata (Keyserling, 1846) Figures 3-1—5 Productus mammatus Keyserling, 1846, p. 206, pl. 4, figs. 5-5b ; Koninck, 1847, p. 49, pl. 7, figs. 4a-e ; Tschernyschew, 1902, p. 295, pl. 35, figs. 4-6; Keidel, 1906, p. 367, pl. 12, figs. 5a, Yakovlevia from Japan 91 14 Figure 3. 1-5. Yakovlevia mammata (Keyserling). 1,2. External mould of a brachial valve and the latex cast, NU-B166. 3-5. latex cast of a pedicle valve exterior, external mould of a brachial valve and the latex cast, NU- B165. 6. Yakovlevia mammatiformis (Fredericks), external mould of a brachial valve, IGPS coll. cat. no. 86649. 7 —15. Yakovlevia kaluzinensis Fredericks. 7—9. internal moulds of pedicle valve specimens, 7. NU-B158, 8. NU- B160, 9. NU-B159. 10,11. external mould of a pedicle valve and the latex cast, NU-B157 ; 12. external mould of a brachial valve, NU-B162 ; 13,14. external mould of a brachial valve and the latex cast, NU-B163. 15. external mould of a brachial valve, NU-B161. (All figures in natural size) b. Muirwoodia mammata (Keyserling). Muir-Wood and Cooper, Linoproductus ? mammatus (Keyserling). Chao, 1927, p. 146, pl. 1960, pl. 120, figs. 9-11 ; Harker in Harker and Thorsteinsson, 15, figs. 10-14. 1960, p. 58, pl. 16, figs. 1-5 ; Gobbett, 1963, p. 112, pl. 18, figs. Productus (Linoproductus ?) mammatus Keyserling. Grabau, 23-28 ; Lee and Gu, 1976, p. 263, pl. 159, figs. 7-9; pl. 163, 1931, p. 288, pl. 29, figs. 10-14. figs. 2a,b; pl.164, figs. 3-4; pl.170, figs. 6,7; Licharew Productus (Thomasina) mammatus Keyserling. Stepanov, 1937, and Kotljar, 1978, pl. 14, figs. 3-5 ; Liu and Waterhouse, 1985, p. 127,177, pl. 2, figs. 5-7. p. 17, pl. 4, figs. 4-6 ; Nakamura et al., 1992, pl. 1, figs. 4a, b ; 92 Jun-ichi Tazawa Kalashnikov, 1993, p. 63, pl. 19, figs. 1-3. Yakovlevia mammatus Keyserling. Kotljar, 1961, text-figs. 4-6. Yakovlevia mammata (Keyserling). Brabb and Grant, 1971, p. 16, pl. 1, figs. 9-12, 33-36 ; Ifanova, 1972, p. 121, pl. 7, figs. 4-5; Malkowski, 1988, p. 40, pl. 5, fig. 6; Zhang, 1990, pl. 2, figs. 4,7,9. Yakovlevia paragreenlandica Lee and Gu in Lee et al., 1980, p. 382, pl. 171, figs. 5-7. Muirwoodia sp. Tazawa, 1987, text-fig. 1.6. Material—Two specimens, from the lower Kanokura For- mation of Kamiyasse and Omotematsukawa in the Kesen- numa area, southern Kitakami Mountains (South Kitakami Belt), northeast Japan : (1) external and internal moulds of a pedicle valve, NU-B165 ; (2) an external mould of a brachial valve, NU-B166. Description.—Shell small for genus, transversely subtrap- ezoidal in outline, with greatest width at hinge line ; length 13 mm-+, width 28mm in the pedicle valve specimen (NU- B165); length 16mm, width 29mm in the brachial valve specimen (NU-B166). Pedicle valve moderately and unevenly convex in lateral profile, slightly convex on venter, strongly geniculated, and followed by a short trail. Cardinal extremities acute. Ears large, not clearly demarcated from visceral part. Sulcus narrow and shallow on venter, becoming wide and deep on trail. Brachial valve nearly flat on visceral disc, strongly geniculated, and followed by a short trail. Fold originating at about midvalve, narrow and low on visceral disc, but wide and distinct on trail. External surfaces of both valves ornamented by numerous fine capillae and several weak, irregular, concentric rugae on visceral disc, capillae only on trail; capillae often bifurcated and intercalated, numbering 14-15 capillae in 5mm at midvalve. Pedicle valve interior with large, flabellate diductor scars, occupying posterior half of valve, deeply depressed and bounded by marginal ridges posterolaterally. Other internal structures not observed. Comparison.—The specimen numbered NU-B166, from the lower Kanokura Formation of the southern Kitakami Mountains, was first figured by Tazawa (1987, text-fig. 1.6) as Muirwoodia sp., but is now referred to Yakovlevia mammata (Keyserling, 1846), originally described by Keyserling in 1846 from the Lower Permian (possibly Sakmarian) of the Pechora Land, northern Russia, on the basis of similarities in size, outline and external ornament. Yakovlevia paragreenlandica Lee and Gu (in Lee et al. 1980), from the Middle Permian Dashizhai Formation of Horqin Youyi Qianqi, eastern Inner Mongolia may be con- specific with the present species. The shells described and figured by Grabau (1936, p. 107, pl.6, figs.5-6; pl. 11, figs. 4-6) as Productus mammatus Keyserling from the Maping Limestone in the Guangxi and Guizhou Provinces, South China differ from Y. mammata in having smaller ears and coarser costellae. Both species, Yakovlevia artiensis (Tschernyschew, 1889, p. 279, pl. 7, figs. 29-31) from the Artinskian of the Central Urals and Yakovlevia greenlandica (Dunbar, 1955, p. 108, pl. 16, figs.1-17) from the Middle Permian (Guadalupian) of Central East Greenland are distinguished from the present species by their fewer and coarser costellae. Yakovlevia mammatiformis (Fredericks, 1926) Figure 3-6 Productus mammatiformis Fredericks, 1926, p. 87, pl. 3, figs. 4-6. Yakovlevia mammatiformis Fredericks. Kotljar, 1961, text-figs. 7, 8. Yakovlevia mammatiformis (Fredericks). Mironova, 1964, p. 97, pl., figs. 14a-v ; Zavodowsky and Stepanov in Zavodowsky et al., 1970, p. 114, pl. 35, figs. 8-10 ; Ifanova, 1972, p. 119, pl. 6, figs. 15-16 ; pl. 7, figs. 1-2; Kalashnikov, 1983, p. 210, pl. 49, figs. 5, 6,9; Kalashnikov, 1993, p. 61, pl. 16, figs. 1-4. Linoproductus cf. mammatus (Keyserling). Yanagisawa, 1967, p. 88, pl. 2, fig. 7. Muirwoodia mammatiformis (Fredericks). 3, figs. 6a-v. Kulikov, 1974, p. 89, pl. Material —One specimen, an external mould of a brachial valve, IGPS coll. cat. no. 86649, from the upper Iriishikura Formation in the Takakurayama area, Abukuma Mountains (South Kitakami Belt), northeast Japan. Description.—Shell medium for genus, transverse, subtrap- ezoidal in outline, with greatest width at hinge line ; length 22 mm, width 42 mm in the brachial valve specimen. Brachial valve gently concave on visceral disc, strongly geniculated at anterior margin of visceral disc, and followed by a short trail. Ears large, flat and prominent, obscurely demarcated from visceral disc. Fold moderately high, originating at about midvalve, and rapidly widening anteriorly. External surface of brachial valve ornamented by numerous fine costellae ; costellae rounded, with narrow interspaces, numbering 10-11 costellae in 5mm at midvalve. No spines or spine bases observed. Comparison.—The single specimen from the Abukuma Mountains was first described by Yanagisawa (1967, p. 88) as Linoproductus cf. mammatus (Keyserling), but this specimen is referred to Yakovlevia mammatiformis (Fredericks, 1926) on the basis of its size, shape and surface ornament of the brachial valve. Yakovlevia mammata (Keyserling, 1846) differs from Y. mammatiformis in its smaller and less transverse shell, ornamented by more numerous, fine capillae. Yakovlevia transversa (Cooper, 1957, p. 39, pl. 5, figs. 1-13) from the Middle Permian of Oregon resembles Y. mam- matiformis in general appearance, but the former is distin- guished from the latter by its smaller dimensions, more developed fold commencing a little below the umbo, and fewer and coarser costellae on the brachial valve. The shells described as Y. mammatiformis from the Middle Permian of Gansu, Northwest China (Ding and Qi in Zhang et al., 1983, p. 292, pl. 99, figs. 9a, b), Inner Mongolia, North China (Lee and Gu, 1976, p. 264, pl. 164, figs. 6,8; pl. 165, figs. 1,5) and Heilongjiang, Northeast China (Lee et al., 1980, p. 383, pl. 165, figs. 25a, b; pl. 172, fig. 3) are distinguished from the present species by their much larger size. Acknowledgements | thank Guang R. Shi of Deakin University, Melbourne, Yakovlevia from Japan 93 Australia for critical reading of the manuscript ; Ei Horikoshi of Toyama University, Yukio Miyake of Miya-mura, Gifu Prefecture and Hiroyuki Ohta of Adachi-ku, Tokyo for providing some of the brachiopod specimens. References cited Brabb, E.E. and Grant, R.E., 1971: Stratigraphy and paleontology of the revised type section for the Tahkan- dit Limestone (Permian) in east-central Alaska. U.S. Geological Survey Professional Paper, no. 703, p. 1-26, pls. 1, 2. Chao, Y.T., 1927: Productidae of China, Pt. 1. Producti. Palaeontologia Sinica, Ser. B, vol. 5, fasc. 2, p. 1-244, pls. 1-16. Cooper, G.A., 1957: Permian brachiopods from central Oregon. Smithsonian Miscellaneous Collections, vol. 134, no. 12, p. 1-79, pls. 1-12. Cooper, G. A. and Grant, R. E., 1975: Permian brachiopods of West Texas, 3. Smithsonian Contributions to Paleobiology, no. 19, p. 795-1921, pls. 192-502. 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In, Xian Institute of Geology and Mineral Resources, ed., Palaeontological atlas of Northwest China; Shaanxi, Gansu and Ningxia volume, Pt. 2. Upper Palaeozoic, p. 244-425, pls. 88-143, Geological Publishing House, Beijing. (in Chinese) Ziegler, A. M., Hulver, M.L. and Rowley, D.B., 1996: Per- mian world topography and climate. In, Martini, |. P., ed., Late glacial and postglacial environmental changes Quaternary, Carboniferous-Permian and Proterozoic, p. 1-37, Oxford University Press, New York. Paleontological Research, vol. 3, no. 2, pp. 95-105, 7 Figs., June 30, 1999 © by the Palaeontological Society of Japan Taxonomy and distribution of Macoma (Rexithaerus) (Bivalvia: Tellinidae) in the northwestern Pacific KAZUTAKA AMANO’, KONSTANTIN A. LUTAENKO’ and TAKASHI MATSUBARA’ ‘Department of Geoscience, Joetsu University of Education, 1 Yamayashiki, Joetsu, Niigata 943-8512, Japan “Institute of Marine Biology, Far East Branch of the Russian Academy of Sciences, Vladivostok 690041, Russia “Division of Earth Sciences, Museum of Nature and Human Activities, Hyogo, 6 Yayoigaoka, Sanda, Hyogo 669-1546, Japan Received 9 March 1999 ; Revised manuscript accepted 30 March 1999 Abstract. Fossil and Recent Macoma (Rexithaerus) of the northwestern Pacific consist of the following three species: Macoma (Rexithaerus) hokkaidoensis sp. nov., M. (R.) sectior Oyama and M. (R.) shiratori- ensis (Matsubara). Among them, the first species, which is new, is characterized by an elongate shell shape and a low pallial sinus, and is now living in the sea around Hokkaido, Kunashiri Island, Aniva Bay of Sakhalin, Peter the Great Bay and Ussuri Bay of Primorye. The oldest species, M. (R.) shiratoriensis appeared in subtropical waters in the late early Miocene. The Recent and allied species, M. (R.) sectior and M. (R.) cf. hokkaidoensis first occurred in middle Miocene deposits. From the middle Miocene to early Pleistocene, the subgenus was confined to the mild- to cool-temperate realm. In the Holocene, M. (R.) sectior has extended its range to subtropical waters, while M. (R.) hokkaidoensis now inhabits the cool-temperate to subarctic waters. Key words: Distribution, Macoma, Rexithaerus, Macoma (Rexithaerus) hokkaidoensis sp. nov., taxonomy Introduction Rexithaerus Tryon, 1869 is a subgenus of Macoma Leach, 1819 and is characterized by a ridge running from beak to posteroventral corner, a bluntly truncated posterior end, a short, rather strong ligamental ridge, and upwardly elevated posterodorsal margin behind ligament. Two Recent species of the subgenus, Macoma (Rexithae- rus) secta (Conrad) and M. (R.) indentata Carpenter, are known from the northeastern Pacific (Coan, 1971). Macoma expansa Carpenter was also included in the subgenus Rexithaerus by Coan (1971). However, M. expansa Carpen- ter and a related species, M. dexioptera Baxter, 1977 do not belong to the subgenus Rexithaerus because they do not have the posterodorsal margin set off as a flange. On the other hand, only one Recent form in this subgenus, “M. (R.) sectior" Oyama, has been recorded from around the Japanese Islands, Korea and Far East Russia in the north- western Pacific (Habe, 1977; Kwon et al., 1993; Kafanov and Lutaenko, 1996). As a result of our review of the both living and fossil specimens from Japan and adjacent areas, we found a new living species of Macoma (Rexithaerus) from southern Hok- kaido, Aniva Bay of Sakhalin and Primorye in Far East Russia, and Kunashiri Island. Macoma (Rexithaerus) originated in northwestern North America in late Oligocene time and migrated westward into Far East Asia during the late early Miocene (Matsubara, 1994). Recently it has been revealed that many molluscan groups show such a pattern of migration (Amano et al., 1993 ; Amano and Vermeij, 1998). However, little is known of the details of the process of climatological adaptation in these groups because most of the westward-spreading species have scattered fossil records owing to their rocky shore habitat. As the subgenus Rexithaerus lives in muddy bot- toms, it is well suited for examining the above biogeographic invasion. In this paper, we discuss the taxonomy of Macoma (Rexi- thaerus) in the northwestern Pacific in addition to the description of the new species. Based on the temporal and spatial distributions of Macoma (Rexithaerus), we will review the climatological adaptation of this genus after its migration to the Northwest Pacific. Materials and methods We have examined specimens of fossil and Recent species stored at Joetsu University of Education (JUE), Museum of Natural History, Tohoku University (IGPS), Sendai, Museum of Nature and Human Activities, Hyogo (MNHAH), Museum of Institute of Marine Biology (MIMB), and Zoologi- cal Museum, Far East State University (ZMFU), Vladivostok. 96 Kazutaka Amano et al. @M. (R-) hokkaidoensis T: type locality AM. (R.) sectior Figure 1. Recent specimens of Macoma (Rexithaerus). Locality map of the treated or illustrated Concerning the new species, we have examined twenty- one right valves and seventeen left valves from the beach of Oshamanbe and Yufutsu along Funka Bay, Hokkaido, one specimen from the Pleistocene Narita Formation in Chiba Prefecture, and two fossil specimens from the upper middle Miocene Shibiutan Formation of Hokkaido (Figure 1). These specimens are all stored in JUE other than one Narita specimen, which is stored in IGPS. In addition, we also have examined seven right valves and eight left valves of the new form collected from the beach of Peter the Great Bay in Primorye (Figure 1). These are housed in ZMFU. Unfortu- nately, all materials were empty shells ; we could not exam- ine the soft parts. For comparison with the above specimens, many Recent specimens of Macoma (Rexithaerus) sectior Oyama were examined from the following localities at hand and stored in IGPS and MNHAH: Katsuori (Ibaraki Pref.) ; Kagamigaura and Kazusa-Onjuku (Chiba Pref.); Kamakura and Zushi (Kanagawa Pref.); Mikawa-Isshiki (Aichi Pref.); Ise (Mie Pref.); Kushimoto and Shionomisaki (Wakayama Pref.) ; Ashiya (Fukuoka Pref.) ; Oga (Akita Pref.) ; Kakizaki (Niigata Pref.) ; and Pohang City and Kallam Village (South Korea). We measured the following characters : shell length, shell height, shell depth, length of pallial sinus (PL) and height of pallial sinus (PH) (see Figure 2). Figure 2. Measurement position. Description of Northwestern Pacific species Family Tellinidae de Blainville Subfamily Macominae Olsson Genus Macoma Leach, 1819 Type species.—Macoma tenera Leach, 1819 by monotypy (= Tellina calcarea Gmelin, 1791). Subgenus Rexithaerus Tryon, 1869 Type species.—Tellina secta Conrad, 1837, by subsequent designation of Dall, 1900. Macoma (Rexithaerus) hokkaidoensis Amano and Lutaenko sp. nov. [Japanese name : Yezo-sagigai | Figures 3—1-3, 5-6, 8; 4—6 Macoma sectior Oyama. Evseev, 1981, pl. 8, figs. 10,12. [non Oyama, 1950] Macoma (Rexithaerus) sectior Oyama. Kafanov and Lutaenko, 1996, p. 16-18, figs. 2a, c, 5, 6. [non Oyama, 1950] Type specimens.—JUE no.15652 (Holotype); JUE no. 15653, 15654 (Paratypes). Type locality —Oshamanbe, Hokkaido, Recent. Description.—Shell of medium size (attaining 63.1mm in shell length), rather thick, elongate-ovate, inflated, in- equilateral, inequivalve ; beak situated slightly posteriorly ; orthogyrate or weakly opisthocline ; posterior Commissure line strongly flexed toward right valve; posterior part moderately gaping; periostracum thin, brownish gray in = Figure3. 1-3,5,6,8: Macoma (Rexithaerus) hokkaidoensis Amano and Lutaenko, sp. nov. 1, 5a-b, 6a-b; JUE no. 15652 (Holotype), Oshamanbe (Recent). 2a-b; IGPS no. 13981, Yamada, Chiba Pref., Narita Formation. 3a-b ; ZMFU no. 9324/Bv-220, Gornostay Inlet of Ussuri Bay (Peter the Great Bay; Recent). 8a-b; ZMFU no. 10003/Bv-474, Kievka Bay (60 km east of Nakhodka; Recent). 4, 7: Macoma (Rexithaerus) sectior Oyama. 4; MIMB no. 2404, Kallam Village near Samchok City, South Korea (Recent). natural in size. 7a-b; JUE no. 15660, Hossaku, Chiba Prefecture, Narita Formation. All figures Northwestern Pacific Macoma (Rexithaerus) 97 Kazutaka Amano et al. Table 1. Measurements (in mm) of Macoma (Rexithaerus) hokkaidoensis Amano and Lutaenko, sp. nov. Specimens Length Height PIE PH* Valve JUE no. 15652 (Holotype) 57.4 38.0 24.5 13.0 Right „ 56.6 87.5 26.0 14.8 Left JUE no. 15653 (Paratype) 51.7 34.8 22.9 13.4 Right JUE no. 15654 (Paratype) 61.6 38.6 26.5 15.8 Left JUE no. 15655-1 54.4 36.4 25.1 13.3 Right JUE no. 15655-2 50.7 32.9 23.0 12.1 Right JUE no. 15655-3 49.7 34.1 22.1 12.2 Right JUE no. 15655-4 53.5 35.2 25.1 13.5 Right JUE no. 15655-5 53.5 34.7 22.0 12.8 Right JUE no. 15655-6 59.1 38.9 25.0 14.2 Right JUE no. 15655-8 54.9 36.8 24.5 13.7 Right JUE no. 15655-9 63.1 40.9 29.2 15.5 Right JUE no. 15655-10 61.1 39.7 28.2 14.0 Right JUE no. 15655-11 57.5 | 37.0 25.0 14.1 Right JUE no. 15655-12 51.8 | 35:3 24.4 14.3 Right JUE no. 15655-13 59.9 40.0 27.4 16.4 Right JUE no. 15655-14 53.4 36.2 24.2 13.9 Right JUE no. 15655-15 48.0 32.2 23.0 13.9 Right JUE no. 15655-16 48.0 32.3 2183 12.3 Right JUE no. 15655-17 47.8 | 31.1 21a 11.8 Right JUE no. 15655-18 | 42.9 | 28.5 19.8 ala Right JUE no. 15655-19 | 43.3 26.7 | 19.3 deal Right JUE no. 15655-22 | 57.5 | 38.1 | 25.0 14.0 Left JUE no. 15655-23 | 57.6 | 36.8 [NN 25;7 15.1 Left JUE no. 15655-24 | 56.0 | 36.4 24.7 15.0 Left JUE no. 15655-25 | 53.9 | 34.5 | 25.9 13.9 Left JUE no. 15655-26 | 50.6 33.4 24.2 14.4 Left JUE no. 15655-27 52.6 | 35.1 25.6 15.8 Left JUE no. 15655-28 | 49.4 | 31.9 24.0 13.6 Left JUE no. 15655-29 | 46.2 29.9 22.1 11.1 Left JUE no. 15655-30 49.7 | 32.4 | 23.9 13.0 Left JUE no. 15655-31 47.2 31.6 | 23.2 14.3 Left JUE no. 15655-32 47.4 30.4 24.3 14.2 Left JUE no. 15655-33 46.9 30.2 23.0 | 12.2 Left JUE no. 15655-34 41.7 27.4 | 20.2 11.6 Left JUE no. 15656-1 36.6 24.6 16.1 9.2 Right | 36.7 23.9 18.2 10.1 Left JUE no. 15656-2 56.0 37.2 27.1 14.8 Left ZMFU no. 220 56.1 38.8 | 26.9 | 15.3 Right ZMFU no. 1621 44.1 30.2 | 21.8 12.3 Right ZMFU no. 1553 42.3 29.1 2158 10.3 Right ZMFU no. 23407 60.4 40.0 28.5 16.6 | Left ZMFU no. 474 56.9 39.2 26.2 15.5 | Right „ 56.1 39.1 26.7 | 15.9 Left ZMFU no. 1215 42.1 28.3 20.9 11.5 Left * PL=length of pallial sinus ; PH=height of pallial sinus. See Fig. 2. + Figure4. 1,3,5: Macoma (Rexithaerus) sectior Oyama. 1a-b, 3a-b; JUE no.15657, Zushi, Kanagawa Prefecture (Recent). 5; JUE no. 15661, Kakuma, Ishikawa Prefecture, Omma Formation. 2a-b: Macoma (Rexithaerus) secta (Conrad) ; JUE no. 15662, Monterey Bay, California (Recent). 4: Macoma (Rexithaerus) cf. hokkaidoensis Amano and Lutaenko, sp. nov. ; JUE no. 15659, Kami-tokushibetsu, Hokkaido, Shibiutan Formation. 7-9: Macoma (Rexithaerus) shiratoriensis (Ma- tsubara). 7a-b, 9a-b; IGPS no. 102563 (Paratypes), Shiratori, Iwate Prefecture, Kadonosawa Formation. 8; IGPS no. 102562 (Holotype), Shiratori, lwate Prefecture, Kadonosawa Formation. All figures natural size. Northwestern Pacific Macoma (Rexithaerus) 99 100 Kazutaka Amano et al. 45 oo ———— ———— = ——— — r “ 1 40 7 | —e— M. hokkaidoensis u. = 7 E — #& - M. sectior 4 ue were 35 — M. shiratoriensis “Te Pe Ë FE | 698 = 30 0977 E ak E Ë Le = 25 5 weg D CT 2 20 F a E a —— H=0.64L+0.93 A= 0.977 15 5 a 4 F ye — -H=0.75L -1.70 R= 0.996 10 | —# 5 bs ot ln, tr Sn 4 ı N 10 20 30 40 50 60 70 Length (mm) Figure 5. Relation between shell length and shell height. GREC or x e— M. hokkaidoensis Seo 14 “- - M. sectior x nine à . M. shiratoriensis CA . — 4 . = 12 Pp, E re . IE 10 + a PH=0.66PL-2.12 R= 0.922 8 * PH=0.71PL-1.30 R= 0.984 PL (mm) Figure 6. Relation between length of pallial sinus (PL) and height of pallial sinus (PH) of left valve. color ; nymph short, produced. Right valve moderately inflated; a strong ridge running from beak to posterior corner ; area in front of ridge distinctly concave, especially near ventral margin ; anterodorsal mar- gin broadly arcuate ; posterodorsal margin behind ligament upwardly elevated forming dorsal flange; posterior margin obliquely truncated ; anterior muscle scar elongated oblong and its inner margin undulated ; posterior muscle scar subovate ; pallial sinus deep, low ovate in shape, and slightly concave between highest and deepest end of pallial sinus ; hinge plate rather wide; anterior cardinal tooth thin and smooth ; posterior cardinal tooth large and subdivided by a distinct groove. Left valve less inflated ; a very weak ridge running from beak to posteroventral corner; a shallow groove running along just posterior part of ridge ; anterodorsal margin broad- ly arcuate ; posterodorsal margin behind ligament slightly upwardly elevated forming dorsal flange ; posterior margin obliquely subtruncated ; ventral margin broadly arcuate and excavated just before posteroventral corner ; posteroventral corner bluntly pointed ; anterior muscle scar deeply impress- ed, elongated oblong and its inner margin undulated ; poste- rior muscle scar subcircular ; pallial sinus deep, but low ovate in shape; anterior cardinal tooth elevated and sub- divided by deep groove ; posterior cardinal tooth very thin, inclined posteriorly and smooth. Remarks.—The present species had already been illus- trated as Macoma sectior Oyama from the Primorye region (Holocene and Recent), Russia (Evseev, 1981; Kafanov and Lutaenko, 1996). The previously figured specimens have a transversely elongate shell, obliquely truncated posterodorsal margin, less prominent dorsal flange, and low pallial sinus shape. Based on these characteristics, they are referred to the present new species. Rexithaerus cf. sectior (Oyama) was recorded from the Middle Miocene Shibiutan Formation of northeastern Hok- kaido by Fujimoto et al. (1998). Some specimens at hand (e.g. JUE no. 15659, see Figure 4—4) from this formation have an elongated shell with obliquely truncated posterior margin, a strong posterior ridge and low ovate pallial sinus, which are in common with the new species. However, it is difficult for them to be exactly identified with Macoma (Rexithaerus) hokkaidoensis because the shell material had eroded out. Thus, we compare the specimens from the Shibiutan Forma- tion with the present new species. Comparison.—The living species, Macoma (Rexithaerus) sectior Oyama, 1950, differs from M. (R.) hokkaidoensis by having a less elongated shell (Table1; Figure 5), higher pallial sinus of both right and left valves (Figure 6), vertically truncated posterior margin, no concave area in front of the posterior ridge, a narrower hinge plate and a prominent dorsal flange. It is especially easy to distinguish the left valves of the two species by the shapes of the posterior part and pallial sinus. Macoma (Rexithaerus) shiratoriensis was described from the uppermost lower to lower middle Miocene Kadonosawa Formation in lwate Prefecture by one of the authors (Ma- tsubara, 1994). This species closely resembles the present new one in its low pallial sinus (Figure 6), less prominent flange and obliquely truncated posterior margin. However, the straight line between the deepest and highest points of the pallial sinus, the higher shell and the concave area in front of the posterior ridge distinguish M. (R.) shiratoriensis from the present new species. Macoma (Rexithaerus) indentata Carpenter, 1864, a Recent species of Northwest America, is similar to the present new species in its protruded posterior part and its elongated shell form. However, it is easy to distinguish the two species by comparing the pallial sinus shape. M. (R.) indentata has a much higher pallial sinus than M. (R.) hokkaidoensis. More- over, M. (R.) indentata has a more elongate shell with a distinct depressed area in the posteroventral part of the shell, and a bill-like posterior end. Right valve of M. (R.) indentata has a pronounced flexure of gully-like type on the surface much deeper than in M. (R.) hokkaidoensis. Macoma (Rexithaerus) indentata flagleri Etherington, 1931, described from the lower middle Miocene Astoria Formation of Washington, is an allied subspecies in its shell outline. However, M. (R.) i. flagleri lacks the pointed posteroventral corner. Unfortunately, we could not compare the internal shell characters of this subspecies because no description of the interior of the shell has been published. Measurements (in mm).—See Table 1. Northwestern Pacific Macoma (Rexithaerus) 101 Distribution —Late middle Miocene: Shibiutan Formation of Hokkaido (cf.). Pleistocene: Narita Formation in Chiba Prefecture. Recent: Oshamanbe and Yufutsu in Hokkaido, Aniva Bay in Sakhalin, Kunashiri Is., Peter the Great Bay and Ussuri Bay in Primorye, Russia. Macoma (Rexithaerus) sectior Oyama, 1950 [Japanese name : Sagigai] Figures 3—4, 7; 4—1,3,5 Macoma secta (Conrad). Yokoyama, 1922, p. 143-144, pl. 11, fig. 1; Nomura, 1938, p. 263-264, pl. 36, figs. 5, 6. [non Conrad, 1837 | Macoma (Rexithaerus) sectior Oyama, 1950, p.3; Kira, 1954, p. 160, pl. 60, fig. 26; Yamamoto and Habe, 1959, p. 106, pl. 9, figs.1,2 ; Kaseno and Matsuura, 1965, pl. 17, figs. 10, 11; Habe and Kosuge, 1967, p. 163, pl. 61, fig. 24; Ohara, 1971, pl. Q-10, figs. 5a-b; Habe, 1977, p. 210, pl. 42, figs. 11,12; Matsuura, 1985, pl. 42, fig. 15; Fujii and Shimizu, 1991, pl. 1, fig. 20 ; Fukuda et al., 1992, p. 91, pl. 34, fig. 538 ; Izawa and Matsuoka, 1996, p. 8, pl. 6, fig. 9. Macoma hokiensis Akutsu, 1964, p. 287-288, pl. 60, fig. 8. Rexithaerus sectior Oyama. Chiba-ken Chigaku Kyoiku Ken- kyu-kai, 1968, pl. 12, figs. 10a-b ; Kuroda et al., 1971, p. 697 (in Japanese), p. 458-459 (in English), pl. 100, fig. 5; Oyama, 1973, p. 113, pl. 52, figs. 14a-b ; Ogasawara, 1977, p. 122-123, pl.14, figs.5a-b, 7; Koyama et al. eds., 1981, p.134 ; Ogasawara et al., 1986, pl. 74, figs. 9a-b; Ishii, 1987, p. 14, pl.12, figs. 12a-b ; Baba, 1990, p. 289; Baba, 1992, p. 540, pl. 69, fig. 11; Matsubara, 1994, pl. 2, figs. 6a-b, 7a-b. Macoma sectior Oyama. Okutani and Habe, 1983, p. 139, 215; Nemoto and Akimoto, 1990, p. 42, pl. 11, fig. 7 ; Kondo, 1991, fig. 3-4. Macoma (Rexithaerus) sectior (Oyama). 379, figs. 91-6-1, and 91-6-2. Macoma “hokiensis” Akutsu. Matsubara, 1994, pl. 2, fig. 5. non Macoma sectior Oyama. Evseev, 1981, pl. 8, figs. 10, 12. | =Macoma (Rexithaerus) hokkaidoensis sp. nov. | non Rexithaerus sectior Oyama. Ogasawara, 1981, pl.1, fig. 9. | =Macoma (Macoma) tokyoensis Makiyama, 1927 | non Rexithaerus sectior (Oyama). Ogasawara and Naito, 1983, pl. 7, fig. 3. [?=Macoma (Macoma) tokyoensis Makiyama, 1927 | non Macoma (Rexithaerus) sectior Oyama. Kafanov and Lutaenko, 1996, p. 16-18, figs. 2a, c, 5, 6. |=Macoma (Rexi- thaerus) hokkaidoensis sp. nov. | Kwon et al., 1993, p. Type specimen.—UMUT CM21317 (Lectotype, designated herein). Type locality and Formation.—Otake, Narita City, Chiba Prefecture, Narita Formation, Pleistocene. Original description —“Macoma secta” in North America has a large, very high, rather thick shell, which is similar to Nuttallia in shape. On the other hand, the shell of the present new species [M. (R.) sectior| is normal in shape, low, thin, fragile, and does not attain a large size. Posterior ridge of American species is highly elevated while that of the present new species is rather weak. Inner side of posterior end of ligament becomes strongly thickened in American species, whereas that of the present new species does not. Posterior adductor muscle scar is situated rather near beak, and a contacting point between pallial line and sinus is separated from anterior adductor muscle scar. The type specimen was collected from Sagami Bay (Enoshima).” (trans- lated from the Japanese original description) Remarks.—Although Oyama (1950) designated the type locality of the present species as Enoshima in Kanagawa Prefecture, he neither designated nor illustrated the type specimen. In addition, the depository still remains unknown. However, Oyama (1950) did list Macoma secta of Yo- koyama (1922) as a synonym. Consequently, we designate herein the specimen illustrated as Macoma secta by Yo- koyama (1922) as the lectotype. This specimen is registered in the University Museum of the University of Tokyo as CM21317 (Oyama, 1973). Macoma hokiensis Akutsu, 1964, described from the Kanomatazawa Formation in Tochigi Prefecture, is regarded as synonymous with the present species on the basis of its rather high shell and pallial sinus shape (see pl. 2, fig. 5 of Matsubara, 1994). Macoma secta (Conrad) by Otuka (1940), from the lower middle Miocene Wakkauenbetsu Formation of Hokkaido, was recently considered as synonymous with M. (R.) sectior Oyama by Kafanov and Lutaenko (1996). However, at least the specimen shown in pl. 11, fig.1 of Otuka (1940) is not referable to the subgenus Rexithaerus because of its rounded posterior margin and the absence of a posterior ridge. Macoma izurensis illustrated by Masuda and Takegawa (1965), from the Fukuda Formation in Miyagi Prefecture, much resembles the present species in the pallial sinus shape rather than either M. (R.) hokkaidoensis or M. (R.) shiratoriensis. However, it differs in having a more obliquely truncated posterodorsal margin. Thus, we treat the speci- mens of Masuda and Takegawa (1965) as M. (R.) aff. sectior Oyama, although they were questionably referred to M. (R.) shiratoriensis by Matsubara (1994). Comparison.—The present species closely resembles Macoma (Rexithaerus) secta (Conrad, 1837) (Fig. 4—2) known from the western coast of North America. However, M. (R.) sectior is distinguished from M. (R.) secta by having a smaller, lower, less inflated shell. Distribution —Late middle or early late Miocene: Kanomatazawa Formation in Tochigi Prefecture (Akutsu, 1964). Pliocene: Tatsunokuchi Formation in Miyagi Prefec- ture (Nomura, 1938); Mita Formation in Toyama Prefecture (Matsuura, 1985; Fujii and Shimizu, 1991). Early Pleis- tocene : Omma Formation in Ishikawa Prefecture (Kaseno and Matsuura, 1965; Ogasawara, 1977 ; Matsuura, 1985) ; Haizume Formation in Niigata Prefecture (this study) ; Naka- tsu Group in Kanagawa Prefecture (Baba, 1992). Middle to late Pleistocene : Nagahama Formation in Chiba Prefecture (Baba, 1990); Narita Formation in Chiba Prefecture (Yo- koyama, 1922; Chiba-ken Chigaku Kyoiku Kenkyu-kai, 1968 ; Oyama, 1973; Baba, 1990); Kioroshi Formation (7?) in Chiba Prefecture (Kondo, 1991); Semata Formation in Chiba Prefecture (Ohara, 1968); Uji Shell Bed in Ishikawa Prefec- ture (Matsuura, 1985) ; Anden Formation in Akita Prefecture (Ogasawara et al., 1986). Holocene: Yokohama in Kanagawa Prefecture (Matsushima, 1969); Osaka in Osaka Prefecture 102 Kazutaka Amano et al. (Ishii, 1987); Anan in Tokushima Prefecture (Nakao, 1995). Recent: Honshu, Shikoku, Kyushu and South Korea (Higo and Goto, 1993); ? Formosa (Taiwan) (Kuroda, 1941; Wu, 1980). Macoma (Rexithaerus) shiratoriensis (Matsubara, 1994), combin. nov. [Japanese name : Shiratori-sagigai | Figures 4— 7-9 Macoma cf. tokyoensis Makiyama. Ogasawara, 1973, pl. 13, fig. 4. [non Makiyama, 1927] Macoma aomoriensis Nomura. Ogasawara, 1973, pl.13, fig. 9. [non Nomura, 1935] Macoma izurensis (Yokoyama). Ogasawara et al., 1986, pl. 1, figs. 12,18. [non Yokoyama, 1925] Macoma sp. B. Ogasawara and Morita, 1986, pl. 2, figs. 25, 28. Rexithaerus shiratoriensis Matsubara, 1994, p. 24-27, tab. 1, pl. 1, figs. 1, 2, 3a-c, 4a-c, 5a-b, pl. 2, figs. 1a-c, 2, 3, 4. Type specimen.—IGPS no. 102562 (Holotype), 102563-1 to -10 (Paratypes). Type locality.—A small tributary of the Shiratorigawa River, south of Shiratori, Ninohe City, lwate Prefecture. Remarks.—The present species is characterized by its moderate-sized (maximum length 61.4mm), transversely elongate-ovate shell (height/length 0.71 to 0.79) with a rather weakly developed posterior ridge, less elevated dorsal flange, obliquely subtruncated posterodorsal margin and low pallial sinus. All species questionably listed by Matsubara (1994), Macoma cf. tokyoensis and Macoma aomoriensis of Ogasa- wara (1973), and Macoma izurensis of Ogasawara et al. (1986), from the same locality belonging to the Nishikurosawa Formation in Akita Prefecture, are considered to be synony- mous with the present species. On the other hand, Macoma izurensis of Kamada (1962), from the Honya and Nakayama Formations in Fukushima Prefecture, is not referred to the present species. As a result of the reexamination of the hypotypes, it becomes clear that the flange-like posterodor- sal margin in the figures of Kamada (1962) is not original, but is due to matrix covering shell material. Thus, these speci- mens are referred to Macoma (Macoma) izurensis (Yokoyama, 1925) as Kamada (1962) thought. Macoma sp. B of Ogasawara and Morita (1986) from the middle Miocene Yanagawa Formation in Fukushima Prefec- ture is considered to be M. (R.) shiratoriensis based on its transversely elongate ovate shell with obliquely truncated posterodorsal margin. Comparison.—M. (R.) shiratoriensis closely resembles M. (R.) indentata flagleri Etherington, 1931. However, the former species can be distinguished from the latter subspecies by having a larger shell with less distinct growth lines and less developed posterior ridge. As already mentioned, the inter- nal characteristics of M. (R.) indentata flagleri are unavailable and thus an exact comparison is difficult. The present species is easily distinguished from M. (R.) indentata indentata Carpenter, a Recent northeastern Pacific species, by having a weaker ridge, less protruding posterior margin, less compressed posteroventral margin in front of a ridge, and lower pallial sinus. Distribution.—Latest early Miocene : Kadonosawa Forma- tion in Iwate Prefecture (Matsubara, 1994). Latest early- early middle Miocene Nishikurosawa Formation in Akita Prefecture (Ogasawara, 1973; Ogasawara et al, 1986). Early middle Miocene: Yanagawa Formation in Fukushima Prefecture (Ogasawara and Morita, 1986). Temporal and spatial distributions of Macoma (Rexithaerus) in Northwest Pacific The subgenus Rexithaerus was considered to be one of those elements which originated in northwestern North America in late Oligocene and migrated into the Northwest Pacific by the late early Miocene (Matsubara, 1994). The earliest Rexithaerus species in the Northwest Pacific region; M.(R.) shiratoriensis (Matsubara), occurs from the upper lower to lower middle Miocene in formations in northeastern Honshu (Figure 7). According to the climato-paleogeogra- phic map of Ogasawara (1994), this species lived in the subtropical realm, but could not invade the tropical one. The next fossil occurrence is M. (R.) cf. hokkaidoensis from the upper middle Miocene Shibiutan Formation of Hokkaido, described above. According to Fujimoto et al. (1998), the molluscan assemblage including M. (R.) cf. hokkaidoensis is correlated with the upper sublittoral “Pitar’-Anadara Assem- blage of the Lower Togeshita fauna (Amano, 1983, 1986). This fauna occupied the mild- or cool-temperate realm in the middle Miocene of Hokkaido (Ogasawara et al., 1993; Ogasawara, 1994). On the other hand, the earliest fossil record of Macoma (Rexithaerus) sectior Oyama is known from the Kanomata- 130° 140° late early-early middle Miocene OM. (R.) shiratoriensis OM. (R.) sp. VA late middle-late Miocene 4 AM. (R.) sectior YA OM. (R.) cf. hokkaidoensis / Wi Va S AM. (R.) aff. sectior GL x FA) 7 ce? @M. (R.) sp. ae > =) X se Y 20) 47 Pr 40°. = 4 1 — V4 G | Pliocene-early Pleistocene vM. (R.) sectior middle Pleistocene-Holocene @M. (R.) hokkaidoensis aM. ) sectior 30° Figure 7. Distribution of the fossil Macoma (Rexithaerus). Northwestern Pacific Macoma (Rexithaerus) 103 zawa Formation in Tochigi Prefecture (Akutsu, 1964, as Macoma hokiensis). The age of the horizon bearing this species is somewhere between the N. 14 and N. 16 zones of the late middle to early late Miocene based on the plank- tonic foraminiferal data (Saito, 1963; Otsuki and Kitamura, 1986). According to Ogasawara (1994), the Kanomatazawa Formation was deposited in the warm-temperate realm. Macoma secta (Conrad) was recorded from the lower middle Miocene Ilyinskaya and the upper Miocene Ermanovskaya Formations in Kamchatka by Sinelnikova (1976) and Gladen- kov et al. (1984). However, these are referred to Macoma s.s. because the specimens lack the posterior ridge. Pliocene M. (R.) sectior is recorded in the cool- to mild- temperate realm. This species was described from the Tatsunokuchi Formation in Miyagi Prefecture (Nomura, 1938), whose age is the latest Miocene to early Pliocene (Yanagi- sawa, 1990, 1998). On the other hand, M. (R.) sectior was also illustrated by Fujii and Shimizu (1991) from the Mita Formation in Toyama Prefecture. Early Pleistocene records of M. (R.) sectior Oyama exist from the Omma-Manganji fauna recognized in the Japan Sea borderland in central and northern Japan. The distribu- tion of this species is restricted to the Omma-Manganji (proper) and Kanto-type subprovinces of Ogasawara (1986), both of which correspond to the mild-temperate marine climate (Ogasawara, 1994). Thus, M. (R.) sectior in the early Pleistocene was confined to the mild-temperate water. In the Recent, M. (R.) hokkaidoensis lives in the cool- temperate and subarctic shallow waters in Hokkaido, south Sakhalin, south Kurile Islands and Primorye while M. (R.) sectior Oyama lives in the upper sublittoral (10-30 m in depth) of the mild-temperate to subtropical waters around Honshu, Kyushu, Shikoku, and South Korea (Higo and Goto, 1993). After the subgenus Rexithaerus arrived in the northwestern Pacific, it lived in the subtropical realm during the late early to early middle Miocene, or the so-called “Climatic Optimum” age. By the late middle Miocene, the subgenus had adapt- ed to the temperate zone as climates cooled after the “Climatic Optimum”. From the late middle Miocene to the Plio-Pleistocene, the subgenus Rexithaerus lived in the mild- or cool-temperate realm. In the Holocene, M. (R.) sectior extended its range to subtropical waters. Kuroda (1941) and Wu (1980) only listed M. (R.) sectior from Formosa (Taiwan). If this is true, M. (R.) sectior may live in the tropical water. However, there is no illustration of the Formosa specimen. The muricid gastropod genus Ceratosoma, a member of the westward-spreading group, shows a history of expansion similar to that of Rexithaerus. Both Macoma (Rexithaerus) and Ceratostoma invaded the subtropical waters around Japan by the early middle Miocene and adapted to the cool- to mild-temperate zone by the early Pleistocene. After or during the middle to late Pleistocene, their distribution extended southward to subtropical waters (Amano and Vermeij, 1998). On the other hand, one of the same west- ward-spreading muricids, Nucella, only lives in mild-temper- ate to arctic waters (Higo and Goto, 1993). One plausible reason why Nucella did not invade warmer waters may be related to its original adaptation not to the subtropical water as Macoma (Rexitherus) or Ceratostoma, but to the cool- temperate water around Japan in the early middle Miocene (Amano et al., 1993). Acknowledgments We are greatful to Geerat J. Vermeij (Univ. California, Davis) and Eugene V. Coan (Santa Barbara Mus.) for their critical reading of this manuscript. We thank Alexander I. Kafanov (Marine Biol. Inst.), Svetlana M. Darkina (Zool. Mus. of Far East Univ.), Masanori Shimamoto (Tohoku Univ.), Jun Nemoto (Tohoku Univ.) and Reishi Takashima (Tohoku Univ.) for their help in studying the fossil and Recent specimens. References Akutsu, J., 1964: The geology and paleontology of Shiobara and its vicinity, Tochigi Prefecture. 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(in Russian) Tryon, G.W., 1869: Catalogue of the family Tellinidae. American Journal of Conchology, vol. 4, no. 5, p. 72-126. Wu, W.L., 1980: The list of Taiwan bivalve fauna. Quar- terly Journal of Taiwan Museum, vol. 33, nos. 1/2, p. 55- 208. Yamamoto, G. and Habe, T., 1959: Fauna of shell-bearing mollusks in Mutsu Bay. Lamellibranchia (2). Bulletin of the Marine Biology Station of Asamushi, vol. 9, no. 3, p. 85-122, pls. 6-14. Yanagisawa, Y., 1990: Diatom biostratigraphy of the Neogene Sendai Group, northeast Honshu, Japan. Bulletin of the Geological Survey of Japan, vol. 41, no. 1, p. 1-25, pl.1. (in Japanese with English abstract) Yanagisawa, Y., 1998: Diatom biostratigraphy of the Neogene Tatsunokuchi Formation in the western Kita- kami City, Iwate Prefecture, Japan. Research Report of the Iwate Prefectural Museum, vol.14, p. 29-36. (in Japanese with English abstract) Yokoyama, M., 1922: Fossils from the Upper Musashino of Kazusa and Shimosa. Journal of the College of Sci- ence, Tokyo Imperial University, vol. 44, p.1-200+ viii (indices), pls. 1-17. Yokoyama, M., 1925: Molluscan remains from the upper- most part of the Joban Coal-field. Journal of the College of Science, Tokyo Imperial University, vol. 45, p. 1-34, pls. 1-6. Paleontological Research, vol. 3, no. 2, pp. 106-120, 7 Figs., June 30, 1999 © by the Palaeontological Society of Japan The turrilitid ammonoid Mariella from Hokkaido — Part 1 (Studies of the Cretaceous ammonites from Hokkaido and Sakhalin-LXXXV) TATSURO MATSUMOTO’, AKITOSHI INOMA’ and YOSHITARO KAWASHITA’ ‘c/o Department of Earth and Planetary Sciences, Kyushu University, Fukuoka, 812-8581, Japan *Daida 6-29-19, Setagaya, Tokyo, 155-0033, Japan ®Tomatsu-Chiyoda 2-179, Mikasa, 068-2134, Japan Received October 30, 1998 ; Revised manuscript accepted April 5, 1999 Abstract. Three species of the genus Mariella (Turrilitidae) from the Lower Cenomanian (Cretaceous) of Hokkaido are described. They include the two widespread species, M. (M.) dorsetensis (Spath, 1926) and M.(M.) oehlerti (Pervinquiere, 1910). but distinguished from M. (M.) oehlerti. The third species, M.(M.) pacifica sp. nov., is somewhat similar to it is also compared with some other species. The problem of dimorphism in the turrilitid ammonoids is discussed. Key words : Cenomanian, dimorphism, Hokkaido, Mariella, Turrilitidae Introduction Ammonoids of the family Turrilitidae have been recorded from various regions of the world. They occur in the mid Cretaceous (Albian and Cenomanian) and include a number of widespread species which are useful for biostratigraphic zonation and correlation. Some of them are, however, apparently endemic. Turrilitids would be also useful to investigate some aspects of palaeogeography and palaeoenviroments during mid-Cretaceous times. Aside from several stratigraphic papers in which some turrilitid species are listed or briefly mentioned, very few species have been hitherto described from Japan, although such a magnificent example as Turrilites komotai Yabe, 1904 (p.7, pls.1,2) [now referred to Hypoturrilites| was once reported. In our present knowledge ammonoids of the Turrilitidae occur fairly commonly in the mid-Cretaceous sediments of certain biofacies in Hokkaido. A rare but important occurrence of Mesoturrilites from Hokkaido has been recently reported (Matsumoto and Inoma, 1999). More species of the family are to be described successively. In this paper three species of the genus Mariella are described, of which two are well Known and widespread. The third species is regarded as new and has not been known elsewhere. Incidentally, T.M. had opportunities to examine some specimens at the Natural History Museum, London, and several other overseas institutions. Moreover, W. J. Ken- nedy kindly sent several specimens to Kyushu University as reference material. Geographic and stratigraphic setting The specimens dealt with in this paper were obtained mainly from the Soeushinai area [Shumarinai-Soeushinai area by some authors] of the Teshio Mountains, northwest- ern Hokkaido. The Cretaceous strata are exposed in the Shumarinai Valley, the Sounnai Valley and the smaller rivu- lets, such as the Kyoei-Sakin-zawa and the Sanjussen- zawa, which are all tributaries of the River Uryu, and also in the upper reaches of the River Kotanbetsu. This area was geologically mapped by Hashimoto et al. (1965) and has been recently reinvestigated by Nishida et al. (1992, 1993, 1996, 1997, 1998a, 1998b). The localities where megafossils and microfossils were collected are pinpointed in the papers by Matsumoto and Inoma (1975) and Inoma (1980) and, further- more, in a number of route maps of the stratigraphic papers by Nishida et a/. (1992, 1993, 1996-1998a, b). Moreover, a locality guide is to be given as an Appendix to this paper. As has been clarified by the above authors, a thick series of strata comprehensively called the Middle Yezo Subgroup of late Albian through Turonian age is extensively distributed in this area. The conformably underlying Lower Yezo Subgroup and the transitionally overlying Upper Yezo Sub- group are partly observable in the area. In a revised scheme of Nishida et al. (1996, fig. 10) the Middle Yezo Subgroup in this area is lithostratigraphically subdivided into the Members My1 to My8 in ascending order. The Mem- bers My1 and My2, together with the uppermost portion of the Lower Yezo Subgroup, are Upper Albian, the Member My3 is Lower Cenomanian, and the Members My4 and My5 represent the rest of the Cenomanian. The age correlation is based on the assemblage of ammonoid and inoceramid species and also on that of some microfossils (Nishida et al., Mariella from Hokkaido—Part 1 107 1992, 1993, 1996-1998a, b). As there is a lateral change in the lithofacies and thickness of the members from place to place, boundary planes of the successive members may be somewhat diachronous in some Cases. The turrilitid ammonoids have been obtained from the Members My2, My3 (most commonly) and My5 and also the upper part of the Lower Yezo Subgroup. These members consist primarily of mudstones, which are sometimes sandy or have intercalated sandy layers and laminae. Conventions Repository.—The illustrated and/or measured specimens are registered in the following institutions which are indicated by the abbreviated symbols as follows : GK : Type Room, Department of Earth and Planetary Sciences, Kyushu University, Hakozaki, Fukuoka GS : Geological Collections, Faculty of Culture and Education, Saga University, Saga MCM : Mikasa City Museum, Mikasa, Hokkaido TKD : Institute of Geosciences, Tsukuba University, Tsukuba [reconstitution of the Tokyo Kyoiku Daigaku | : University Museum, University of Tokyo, Hongo, Tokyo Morphological terms.—For the morphological terms to describe the turrilitid ammonoids, we. follow those used by Wright and Kennedy (1996). Setting the apex of the turrical shell at the top, the terms upper and lower or adapical and adoral | —abapical] are defined and the rows of tubercles or ribs on the face of each whorl are described in descending order as the first, the second and so on. The term flank (see Forster, 1975) may be used for the exposed whorl face of Wright and Kennedy (1996). Palaeontological descriptions Order Ammonoidea Zittel, 1884 Suborder Ancyloceratina, Wiedmann, 1966 Family Turrilitidae Gill, 1871 Genus Mariella Nowak, 1916 Type species.—Turrilites bergeri Brongniart, 1822 (p. 395, pl. 7, fig. 3) by original designation (Nowak, 1916, p. 10). Remarks.—Wright and Kennedy (1996, p.330) have given an ample generic diagnosis and discussed problems of nomenclature. The genus includes the two subgenera, Mariella (Mariella) Nowak, 1916 and Mariella (Wintonia) Adkins, 1920, the latter of which is a senior synonym of Mariella (Plesioturrilites) Breistroffer, 1953 (See Wright and Kennedy, 1996, p. 331). An undoubted example of M. (Wintonia) has not been so far found from Japan, whereas there are a number of specimens from Hokkaido which are referable to at least eight species of M. (Mariella). Mariella (Mariella) dorsetensis (Spath, 1926) Figure 1 Turrilites bergeri Brongniart. Sharpe, 1857, p. 65, pl. 26, fig. 11 only. Turrilites dorsetensis Spath, 1926, p. 429. Mariella dorsetensis (Spath). Spath, 1937, p. 513; Marcinowski, 1970, p. 431, pl. 3, fig. 1; Seyed-Emami and Aryai, 1981, p. 26, pl. 6, figs. 5, 6. Paraturrilites lewesiensis (Spath). 436 (pars.), pl. 40, figs. 8, 9 (?). Benavides-Cäceres, 1956, p. Figure1. Mariella (Mariella) dorsetensis (Spath). 3a, b. GS. G180, two lateral views (different sides from 1), x2. 4a-c. GS. G182, two lateral and basal views, x 1.5. 1. GS.180, 1. 2a, b. GK. H8504, two lateral views, x 2. 108 Tatsuro Matsumoto et al. Mariella (Mariella) dorsetensis (Spath). Atabekian, 1985, p. 35, pl. 6, figs. 6, 9; Wright and Kennedy, 1996, p. 344, pl. 100, figs. 5,11, 17, 19, 22, 25; pl. 102, fig. 7 ; text-figs. 136B, E (with full synonymy). Holotype.—BMNH. C3834, figured by Sharpe, 1857, pl. 26, fig. 11 and named as Turrilites dorsetensis Spath, 1926, p. 429 (by monotypy). Material. GS. G180 (Figure 1-1, 3) and GS. G181, both from loc. R905 | = YKC080621b |, Hotei-zawa ; GK. H8504 (Figure 1-2) from loc. R518p5, East Suribachi-zawa; GK. H8505 from loc. R438p, GK.H8506 from loc. R433p, and TKD 30081A,B from loc. 81007, in the upper reaches of the Suribachi-zawa ; TKD 30080A-D from loc. 71204 in the middle course of the River Shumarinai ; GS. G182, (Figure 1- 4), from loc. YKC060824, Sanjussen-zawa. These are all from the Lower Cenomanian Member My3 of the Soeushinai area. Description.—The available specimens are all small and incomplete, as seen in the illustration (Figure 1). In general, the apical angle is acute (20-25° in our estimation). The whorl is rounded in section, showing a moderately or broadly convex outer face ; the whorl junction is well defined and crenulated. The tubercles in four rows are of moderate density and number 20 to 25 per whorl in each row. The tubercles on the outer whorl face are disposed slightly obliquely in three rows at subequal intervals and of nearly equal moderate intensity. The tubercle of the first row is elongated upward to a distinct rib on the upper face of the whorl. In some specimens the fourth tubercle is slightly smaller than the others and close to the third one, although it is beyond the lower whorl seam. On the lower whorl face ribs run from the third row tubercles to the narrow umbilicus by way of the fourth row tubercles, showing a gentle curvature. Septal sutures are partly exposed (GK. H8505). Comparison.—The above-described specimens from Hok- kaido are well comparable with the holotype and other examples of M.(M.) dorsetensis from England (Wright and Kennedy, 1996, pl.100, figs. 5, 11,17,19, 22,25) and also previously illustrated specimens from several regions of the world (See synonymy list). Affinities with other allied species are discussed below, together with some remarks on ques- tionable points. Occurrence.—As for material. This species has been reported from the Lower Cenomanian of southern England, northern France, Poland, Turkmenistan, Iran, Madagascar and Peru (See synonymy list). Discussion.—M. (M.) dorsetensis is similar to and could be interpreted as a descendant from M.(M.) bergeri of the uppermost Albian. The apical angle of the former is smaller than that of the latter. In fact the apical angle of M. (M.) bergeri is recorded as 33-38 by Spath (1937, p. 511) and an example of Pictet and Campiche (1862, pl. 58, fig. 2) reillus- trated by Renz (1968, pl. 18, fig. 4) gives 34°, as compared to the 20-25° of M.(M.) dorsetensis. On the average the tubercles are somewhat more crowded and more distinctly connected by longitudinal ribs in M. (M.) bergeri. The relationship between M. (M.) dorsetensis and M. (M.) lewesiensis (Spath, 1926) is a moot problem, as has been discussed by Kennedy (1971, p. 28) and Klinger and Kennedy (1978, p. 31). The difficulty can be guessed from the con- fused state in the lists of synonymy between authors (even between the same palaeontologist writing on different dates) (see Wright and Kennedy, 1996, p. 339-340 and p. 344). Collignon (1964, pl. 331, fig. 1482) has shown an example of M. (M.) dorsetensis with a rostrate last whorl. This suggests the small size of this species. We notice, however, that an example of the same species illustrated by Atabekian (1985, pl. 6, fig. 6, 6b) is nearly as large as the holotype of M.(M.) lewesiensis (see Sharpe, 1857, pl. 20, fig. 10 or Wright and Kennedy, 1996, p. 101, fig. 3). There is no difference in the estimated apical angle between the two species. There may be differences in the ornament. The relative smooth- ness of the upper face of the whorl was regarded as a criterion by which to distinguish M. (M.) lewesiensis from M. (M.) dorsetensis, but some of the coarse tubercles of the first row in the former show faint elongations on a part of the upper whorl face, depending probably on the mode of light- ing (see Kennedy, 1971, pl. 8, figs. 1,4, 5,8). Wright and Kennedy (1996, p. 340) have recently given their opinion that rounded subequal tubercles in the upper two rows plus feeble spiral (i.e. clavate) elongation of the tubercles in the lower two rows characterize M.(M.) lewesiensis. Indeed, the tubercles on the outer whorl face are coarse and globular in M.(M.) lewesiensis and rather granular but transversely elongated in M. (M.) dorsetensis, although there is no marked difference in the number of tubercles to a whorl. For us it is difficult to understand the significance of the “feeble spiral elongation of the lower tubercles’. The tubercles of the lower two rows are Clavate in the holotype, but the feature is not well shown in the illustration of some other specimens (e.g., Wright and Kennedy, 1996, pl. 100, figs. 23, 27). According to Klinger and Kennedy (1978, p. 31, pl. 7, fig. F), in M. (M. lewesiensis | =M. (M.) dorsetensis in their paper] ribs are absent or only a few traces are discernible on the lower whorl face, although they did not give a photograph of the basal view. On the lower whorl face of the holotype ribs are extended very faintly from the tubercles of the fourth row (T.M.'s observation at the Naturat History Museum, London). This character is also shown on some examples of M.(M.) lewesiensis by Atabekian (1985, p. 37, pl. 7, fig.1,1b; pl. 8, fig. 1, 1a), whereas ribs are distinctly developed on the lower whorl face of M.(M.) dorsetensis from the Kopet Dag (see Atabekian, 1985, p.35, pl.6, fig.6,6b) as well as in our specimens (e.g., Figure 1-4 of this paper). If this difference is confirmed in a sufficient number of specimens, it would become one of the reliable criteria to distinguish the two species. So far, an undoubted example of M. (M.) lewesiensis is not found in the material of the Soeushinai area. The speci- mens which were tentatively identified with M. lewesiensis by A.l. (as written on the labels) are actually M.(M.) oehlerti (Pervinauiere). Mariella from Hokkaido—Part 1 109 Mariella (Mariella) oehlerti (Pervinquiere, 1910) Figures 2-4 Turrilites gresslyi Boule, Lemoine and Thevenin, 1907 (non Pictet and Campiche, 1861), p. 57, pl. 18, fig. 2, 2a. Turrilites oehlerti Pervinquiere, 1910, p. 53, pl. 5, figs. 14-17; Collignon, 1929, p. 65, pl. 6, figs. 16, 17 ; Matsumoto, 1938, p. 23, pl. 2, fig. 7; Collignon, 1964, p.15, pl. 320, figs. 1398, 1399. Mariella (Mariella) oehlerti (Pervinquiere, 1910); Forster, 1975, p. 190, pl. 7, figs. 7, 8; text-fig. 52; Atabekian, 1985, p. 30, pl. 6, figs. 4, 5; Wright and Kennedy, 1996, text-fig. 138 J,O,V. Mariella (Mariella) oehlerti oehlerti (Pervinquiere, 1910). Klinger and Kennedy, 1978, p. 31, pl. 3E; pl. 4E ; pl. 6H-N; pl. 7G; pl. 8G-H; text-figs. 1A, B; 7B, D; 8G. Mariella (Mariella) oehlerti sulcata Klinger and Kennedy, 1978, p. 33, pl. 8, fig. D; text-figs. SE, 8H (? non pl. 3D; text-fig. 3D). Holotype.—The specimen figured by Pervinquiere (1910, pl. 5, fig. 16) from the Cenomanian of Aumale, Algeria (by original designation). Klinger and Kennedy's (1978, p. 31) designa- tion of a lectotype (Pervinquiere, 1910, pl. 5, fig. 15) was misleading, and Atabekian (1985, p. 30) erroneously followed them. Material.—A large number of specimens from the Member My3 of the Soeushinai area are referable to this species. The representative ones among them are as follows: GK. H8500 (Figure 2-1) and GK. H8501 obtained by T.M. at loc. R518p5 and GS. 166 (Figure 2-7) collected by Y.K. at loc. R518p! from the East Suribachi-zawa ; TKD 30086A (Figure 3-2), TDK 30086B (Figure 3-3) and TKD 30086C (Figure 2-6) obtained by A.l. from a nodule at loc. 81001 in the Suribachi- zawa; TKD 30546B (Figure 2-2) and A collected by W. Hashimoto from a nodule at loc. P2 in the River Shumarinai and provided to A.l. for study ; GS. G163 (Figure 2-3) and GS. G164 (Figure 2-4) collected by Y.K. at loc. YKC060824 in the Sanjussen-zawa ; GS. G165 (Figure 2-5) collected by Y.K. at loc. YKC050610 in the Bishamon-zawa ; GS. G167 (Figure 3- 1) collected by Y.K. at loc. YKC591014 and also GS. G168 (Figure 4-1) and GS. G169 (Figure 4-2) collected by Y.K. at loc. YKC020619 in the Kyoei-Sakin-zawa. Description.—Although completely preserved specimens are hard to come by larger examples are approximately estimated at 250mm in total whorl height and 70mm in diameter of the last whorl. Several specimens which pre- serve the rostrum suggest a size dimorphism. The above larger ones, as represented by GS. G168 (Figure 4-1), may represent a macroconch, whereas GS. G167 (Figure 3-1) and TKD 30086A, B (Figure 3-2, 3) may be microconchs, for they are half of the macroconch in size. The rostrate peristome of a larger form, exemplified by GS. G169 (Figure 4-2), is twice as large as that of a smaller form, e.g., TKD 30086C (Figure 2-6). The apical angle is low but seems to be somewhat variable between individuals and probably also with growth. On account of incomplete preservation, the actual angle is hard to measure with precision. It is roughly estimated at 25 (+5) on the average. The whorl is asymmetrically subquadrate to broadly rhom- boidal in section. Its upper flank [i.e. upper part of the exposed whorl face] slopes down, forming an obtusely angular (costal) or a subrounded (intercostal) shoulder at the first row of tubercles ; its middle flank [i.e., main part of the exposed whorl face] is nearly vertical and forms an obtuse shoulder at the second row of tubercles with the narrow, lower flank which inclines steeply inward ; the whorl junction is thus fairly deep and crenulated. The aperture is suboval and provided with a rostrum that extends at first downward and then recurves obliquely upward (See Figures 3-3; 2-6; 4-1, 2). The tubercles are moderate in strength and coarseness ; those of the first row are more prominent than others and extend upward to the ribs on the upper flank. Those of the three rows on the exposed whorl face are nearly equidistant, arranged more or less obliquely and sometimes connected by blunt riblets ; those of the third row may be granular or sometimes rather clavate (i.e. extended spirally); the inter- space between the second and third rows of tubercles is sometimes narrower than that between the first and second rows and, furthermore, it may be grooved to various depths (see Figure 2-5). The tubercles of the fourth row are close to those of the third row in some specimens but they are disposed along the outer margin of the basal part of the whorl. The tubercles of each row in our sample normally number from 20 to 28 to a whorl. TKD 30546B (Figure 2-2) may exemplify an extreme case (30 to a whorl), but it is referred to this species in consideration of other characters. Aside from the bullate extension to the ribs, the tubercles of the upper two rows are conical with a rounded base. In some cases they may preserve a sharply pointed summit, but so far a highly extended spine has not been observed in our material. Near the apertural margin the tubercles are obliquely bullate and extended to gently flexuous narrow ribs. The last rib goes on to form a blunt ridge on the rostrum, whereas the other side of the rostrum is ornamented by very fine and delicate riblets and dots (see Figures 2-6a, b, 4). The septal suture is not well traced in our material, because the internal mould is not well exposed. It was illustrated by Förster (1975, fig. 52) on a young example from Mozambique and partly by Klinger and Kennedy (1978, fig. 1A, B) on middle-aged specimens from South Africa. Comparison and discussion.—As the types originally de- scribed by Pervinquiére (1910) and also the specimens dealt with by subsequent authors up to 1975 are so small it was difficult for us to understand the diagnosis of this species. Based on a great number of specimens from the Lower Cenomanian of South Africa, Klinger and Kennedy (1978) have clarified the diagnosis of this species and also its relations with or distinctions from other species. Wright and Kennedy (1996, text-fig. 138 J,O,V) have finely reillustrated Pervinquiére’s holotype and paratypes. These two works have enlightened us in getting a proper conception of M. (M.) oehlerti. In our material there are specimens which closely conform with the holotype. GK. H8500 (Figure 2-1) is such an exam- ple. They are, however, immature. The full-grown adult shell has a rostrate aperture. The three specimens illus- trated in Figure 3 exemplify the abult shells of moderate size, 110 Tatsuro Matsumoto et al. Figure 2. Mariella (Mariella) oehlerti (Pervinquiere). 1a, b. GK. H8500, two lateral views, 1.2 (The terminal protuberance is not a rostrum but an attached juvenile of Anagaudryceras sp.). 2a-c. TKD 30546B, two lateral and basal views, 1.5. 3. GS.G163, x15. 4. GS.G164, x4/3. 5. GS.G165, 4/3. 6a,b. TKD 30086c, detached rostrum, external and the other sides, «1. 7. GS. G166, a large but incomplete example, 1. Mariella from Hokkaido—Part 1 Figure 3. Mariella (Mariella) oehlerti (Pervinquiére). More or less deformed examples of a smaller form with a rostrate peristome, all «1. 1a-c. GS. G167, three lateral views. 2a,b. TKD 30086A, two lateral views. 3a-c. TKD 300868, three lateral views. 111 112 Tatsuro Matsumoto et al. Figure 4. Mariella (Mariella) oehlerti (Pervinquiére). Examples of a larger form, x0.9. 1a-c. GS. G168, two lateral views (a, b) and aperture (c). 2a, b. GS. G169, two views of a detached rostrum. Mariella from Hokkaido—Part 1 113 although they are considerably affected by secondary defor- mation. Among a number of South African specimens, BMNH C79806 (Klinger and Kennedy, 1978, pl. 6, fig. K) is an illustrated example of the adult stage. It is similar in size to our examples mentioned above, but it preserves only two whorls of the late growth stage. In our material from the Member My3 there are much larger adult specimens which preserve the rostrate oral part. GS. G168 (Figure 4-1) is an example of such a large form. It is nearly twice as large as the specimens mentioned above. GS. G166 (Figure 2-7) is referable to a similarly large form, although its later part is not preserved. GS. G169 (Figure 4- 2) is a detached piece of a rostrate oral part. It is nearly twice as large as TKD30086C (Figure 2-6), which is a detached oral part of a smaller form. The facts described above suggest the existence of a dimorphic pair in this species. To confirm the dimorphism, it is necessary to get further evidence from the materials of other regions. Although “several hundred specimens” of this species from South Africa have been treated by Klinger and Kennedy (1978, p. 32), they did not make mention of the size variation or dimorphism. The specimens figured by them are more or less incomplete, consisting of a few whorls. The largest example among them is BMNH C79860 (op. cit., pl. 8, fig. H). [Note that figure is actually x 5/4, although it was indicated as x1.] It could be comparable with a part of the large specimen (GS. G168, Figure 4-1) from Hokkaido, but it lacks the oral end. On the other hand, a specimen from South Africa (op. cit. pl. 6, fig. K) which possesses an incomplete rostrum is comparable with the smaller form from Hokkaido. Dimorphism in the Turrilitidae has been noted by Wright and Kennedy (1996, p. 349) for Turrilites scheuchzerianus Bosc and certain other species, but Lehmann (1998, p. 37) has given comments and suggested that the observed difference might simply be size variation. There could be, however, size variation in both microconch and macroconch. For a final conclusion one should examine a sufficient number of samples. There is another problem to be discussed. Some speci- mens of M. (M.) oehlerti from the Member My3 of the Soeushinai area show a spiral sulcus between the second and third rows of tubercles. In such cases, the tubercles rest on low ridges and may be obliquely clavate. The groove is thus variable in its degree of distinctness among the specimens and the sulcate specimens often occur together with normal ones. This feature is similar to that already noticed in the material of South Africa. Klinger and Kennedy (1978, p. 33, pl. 3, fig. D; pl. 8, fig. D ; text-figs. 3D, D; 8H) have established a subspecies M. (M.) oehlerti sul- cata. One of us (T.M.) examined some of the specimens labelled as “M. (M.) oehlerti sulcata”, such as BM. C79952 (op. cit., pl. 8, fig. D), C79951, C79950 and C79949. They seem to show a gradual change in morphology from “M. (M.) oehlerti oehlerti” to “M.(M.) oehlerti sulcata.” The holotype of the subspecies M. (M.) oehlerti sulcata Klinger and Kennedy, 1978 is SAS A2908. Although we have yet no opportunity to examine the actual specimen itself, its fine illustration (op. cit., pl. 3, fig. D) gives us a strong impression that it resembles a form of Mesoturrilites aumalensis (Coquand) such as was figured by Pervinquiere (1910, pl. 14, fig. 22) (see Wright and Kennedy, 1996, text-fig. 138 S-T). Furthermore, we see that the specimen in ques- tion (SAS A2908) is similar to, if not identical with, Mariella (Mariella) bicarinata (Kner, 1852) (see Atabekian, 1985, p. 40, pl. 8, figs. 2-9; pl. 9, figs. 1, 2; Wright and Kennedy, 1996, p. 335, pl. 98, figs. 7, 12; pl. 102, fig. 11). We are thus, inclined to consider that it would be better to exclude the holotype of M. (M.) oehlerti sulcata from M. (M.) oehlerti. Incidentally, the above observation may be favourable to the suggestion of Wright and Kennedy (1996, p. 346) to seek the origin of Mesoturrilites in M. (M.) bicarinata. Occurrence.—As for material. In addition, incompletely preserved specimens which can be called M. (M.) cf. oehlerti are found commonly in the Member My3 of the Soeushinai area. At least some of the specimens, including GK. H8500 and H8501, occur in the lower part of the Member My3 together with Graysonites adkinsi Young. Records of this species from other areas in Hokkaido are so far poor, except for a fine specimen MCM A517 collected by Reishi Takashima and Koji Hasegawa from the Oyubari area. This is to be reported in detail on another occasion. Outside of Hokkaido in Japan a few small specimens of this species were described by Matsumoto (1938, p. 23, pl. 2, fig. 7) from the Unit lle of the mid-Cretaceous Goshonoura Group of Kyushu ; Graysonites cf. fountaini Young occurs in the same unit (Matsumoto, 1960, p. 44, pl. 6, fig. 1; pl. 7, figs. 1-4; text-figs. 1-7, with Matsumoto et al., 1960, p. 51). M.(M.) oehlerti has been reported from the Lower Cenomanian of Algeria, Madagascar, Mozambique, South Africa and Turkmenistan (Kopet Dag) (see references in the synonymy list). The record of its occurrence in the Gulf Coast (Texas and Mexico) (Young and Powell, 1978, pl. 8, figs. 4,6) is not clear. As species of Graysonites occur there, undoubted example of M.(M.) oehlerti should be searched for. Mariella (Mariella) pacifica sp. nov. Figure 5 Material. —Holotype is GS. G170 (Figure 5-1) from a nodule contained in the siltsone of the middle part of the Member My3, collected by Y.K. and N. Egashira at loc. R905 of the Hotei-zawa, a branch stream of the River