ISSN 0031-0204 Transactions and Proceedings of the Palaeontological Society of Japan New Series No. 109 Palaeontological Society of Japan April 30, 1978 Editor Itaru HAYAMI Associate editors Tsunemasa SAITO and Tomowo OZAWA Officers for 1977 - 1978 Honorary President: Teiichi KOBAYASHI President: Ryuzo TORIY AMA Councillors: Kazuo ASAMA, Kiyotaka CHINZEI, Takashi HAMADA, Tetsuro HANAI, Itaru HAY AMI, Syozo HAY ASAKA, Hisayoshi IGO, Tadao KAMEl, Kametoshi KANMERA, Tamio KOTAKA, Tatsuro MATSUMOTO, Tsugio SHUTO, Yokichi TAKA YANAGI, Toshimasa TAN AI, Hiroshi UJIIE Members of Standing Committee: Kazuo ASAMA (Finance), Kiyotaka CHINZEI (General Affairs), Takashi HAMADA (Foreign Affairs), Tetsuro HANAI, Ita­ ru HAYAMI (Transactions), Hisayoshi IGO (Planning), Kametoshi KANMERA (Special Papers), Ikuwo OBATA (Membership), Yokichi TAKAYANAGI ("Fossils"), Hiroshi UJIIE, Juichi YANAGIDA Secretaries: Ienori FUJIYAMA (Special Papers), Kunihiro ISHIZAKI ("Fossils"), Tsunemasa SAITO and Tomowo OZAWA (Transactions), Hiromichi HIRANO and Yasumitsu KANIE (Membership), Toshiyuki YAMAGUCHI (General Affairs) Auditor: Tatsuaki KIMURA The fossil on the cover: Original figure of Podozamites Reinii GEYLER, 1877, from the Tetori group. GEYLER'S description marked the onset of modern palaeontology in Japan. All communications relating to this Journal should be addressed to the PALAEONTOLOGICAL SOCIETY OF JAPAN, c/ o Business Center for Academic Societies, Yayoi 2-4-16, Bunkyo-ku, Tokyo 113, Japan. Sole agent: University of Tokyo Press, Hongo 7-3-1, Tokyo, Japan. Trans. Proc. Palaeont. Soc. Japan, N. S., No. 109, pp. 223-2:'4, pis. 31, 32, April 30, 1978 684. DISCOACTINOCERAS AND THE DISCOACTINOCERATIDAE, FAM. NOV.* TEIICHI KOBAYASHI Japan Academy, Tokyo Abstract. Discoactinoceras used to be placed in either the Huroniidae or the Polydesmiidae is quite distinct from them in the growth of intrasiphuncular stereo­ plasmic deposits from the actinoceroid to endoceroid type. Because its septal neck is of Armenoceras type, it must be a derivative from the common stock with the Armenoceratidae. In longitudinal section the septum looks sigmoidal by an adoral and adapical bent respectively near the conch and septal neck. From these distinc­ tions a new family, Discoactinoceratidae, is proposed for the genus. Here, not only Discoactinoceras multiplexum, the type-species of this genus, but also D. cf. multi­ plexum and D. okdongense, nov. from South Korea are described in detail. Discoactinoceras known from South ceras. Therefore a new family, Discoac­ Manchuria and North Korea is an inter­ tinoceratidae, is here established. esting genus having shoulderedn nummuli Judging from the siphuncular structure like the Huroniidae, but its siphuncular this family indicates an aberrant branch structure is very complicated. Because issued from the common stock with the the description of its type-species and Armenoceratidae in the middle Toufan­ generic diagnosis written almost fifty gian or middle Mohawkian age by para­ years ago is inadequate, they are here llel specialization to the Endoceratida by redescribed. Discoactinoceras multiplexum the benthonic adaptation in the grown was monotypic. Five specimens contained stage. in SHIRAKI collection from South Korea represent two forms of this genus for one of which a new name is proposed. Family Discoactinoceratidae, fam. nov. Discoactinoceras has been placed in the Diagnosis:-Actinoceroid with a large Huroniidae or the Polydesmiidae, but marginal siphuncle whose deposits consist either one of them is unable to have it of outer annuli and inner tubular or con­ in its domain principally because of the ical sheathes; septa geniculated in pro­ possession of double structural elements ximal and distal parts; septal neck ar­ of the siphuncle. The family Georginidae menoceroid. recently proposed by WADE; from Aust­ Remarks: - Since FOERSTE and TEI­ ralia also have double elements in its CHERT'S reference (1930) Discoactinoceras siphuncle, but these elements are essenti­ has long been allocated in the Huroniidae, ally different from those of Discoactino- but as detailed below, it is sufficiently * Received June 16, 1977; read Oct. 16, 1977 distinguishable from that family. This at Kumamoto. genus must have been evolved from an 223 224 Teiichi KOBAYASHI unknown common stock with the Armeno­ annuli, but becoming later tubular or ceratidae, but the high specialization re­ conical sheathes; central cavity broad quires its isolation from that family, primarily, but later narrowing and be­ Judging from its complexity of the septa coming tubular; radial canals branching and siphuncle it is quite improbable that off from central cavity or tube and ex­ it is ancestral to the late Ordovician­ tending laterally through sheathes; stereo­ Silurian Huroniidae. Its siphunucular plasmic deposits undeveloped in camerae. structure is incomparable with the radi­ Surface of conch. apical end and body ally disposed longitudinal lamellae or chamber unknown. endosiphuncular blades by TEICHERT and Type-species: - Discoactinoceras 71lulti­ CRICK (1974) in Huroniella servenense plexu11l KOBAYASHI, 1929. (FOERSTE and SA V AGE, 1927). Remarks:-In the large siphuncle with This genus was once located in the shouldered nummuli and septal genicula­ Polydesmiidae by CHAO et al. (1965), but tion this genus resembles Huroniella. It, as I have alreadY detailed that family in however, differs essentially from Hllronia 1940 and 1977, Discoactinoceras has inner and Huroniella in the marginal position tubular sheathes on one side and its an­ of the siphuncle in this genus. The nuli do not grow in horn-shape as in that siphuncular deposits are unusually com­ family on th e other. plicated in this family. The genus was In the Georginidae tubular deposits allocated in the Polydesmiidae (CHAO et called endocones by VI' ADE (1977) some­ aI., 1965), but the siphunclar structure of times appear in the central cavity of that family is quite different from that Georgina and well developed in the cavity of this family. of iv!esaktoceras like in Discoactinoceras. The septa of this genus is more or In the radially lamellate structure of the less' sigmoidal, although its middle main nummulus and particularly in the so-called part is nearly straight. The sigmoidal engraft by VI' ADE, however, that family septa may be comparable to those of is quite distinctive. Gonioceras, but it is no more than a paral­ Thus. Discoactinoceras is isolated from lelism in the trend of specialization. the Huroniidae, Polydesmiidae, Georgin­ because Gonioceras is quite different in idae, or else in the Actino ceratida in most other characteristics. its double structure in the inner and Recently CHEN and LIU (1976) described outer parts of the siphuncle so far two new species of Discoactinoceras, that a new family should be instituted platyventrum and wuyangshanense, from for it. the middle part of their Machiakou suite Distribution :-Middle Ordovician; East­ in Shantung. The latter species appears ern Asia. to resemble D. okdongense, while the former is quite distinct from Discoac­ Genus Discoactinoceras KOBA YASH!, 1929 tinoceras in the Actinoceras-type septal neck and especially in the structure in Diagnosis: - Orthoconic actinoceroid the inner part of the siphuncle. with large marginal siphuncIe; septa Distribution:-Toufangian and its cor­ geniculated near siphuncle and shell wall; relatives in Korea, North China and septal neck armenoceroid ; siphuncular seg­ Southern Northeast China. ment very wide, shouldered near septal Recently CHEN and LIU (1976) distin­ neck; siphuncular deposits beginning with guished the Discoactinoceras- Loplwspira 684. Discoactinoceras and the Discoactinoceratidae 225 yentaiensis zone in the middle part of the Dawan formation and the Neichiashan their Machiakou suite in North China series of Central and South China where and Northeast China and considered the .series was subdivided into the Kuni­ Llanvirnian. Because their Machiakou utan limestone, Miaopa shale and Pagoda suite easily confuses the traditional Ma­ limestone in ascending order (CHANG, chiakou limestone, a few words are added 1964). According to Lu (1975) the Dawan here. formation is Llanvirnian plus the Azygo­ Ordovician rocks in North China were graptus suecicus zone and the .Neichiashan first classified in about 1921 into the series Llandeilian-middle Caradocian Yehli formation, Liangchiashan limestone (Sinoceras sinense zone) in age. and Machiakou limestone in ascending According to CHEN (1976) the post­ order, and the Machaikou fauna was Liangchiashan rocks of North China, correlated with the Black River or Mohaw­ namely the traditional Machiakou lime­ kian of North American by GRABAU stone, is classifiable into four suites, re­ (1922). This tripartition has long been stricting the Machiakou suite to a part in current use in China. but the Machia­ of the limestone and they are correlated kou limestone was subdivided into two to the North American sequence as be­ parts. The lower and upper Machiakou low. limestone were correlated respectively to Suite Cephalopod zone North American correlative Patou Gonioceras badonellse Mohawkian Kechuang None Tofangoceras pauciannulatum Machiakou Stereoplasmoceras pseudoseptum Chazyan Ordosoceras quasililleatum Peianchuang Polydesmia zuezshanensis Whiterock Subsequently, however, the Discoac­ tive. Incidentally, lower Chazy an or tinoceras-Lophospira yentaiensis zone was Whiterock of today is approximate to added at the middle part of the Machia­ Llanvirnian. while