Trans. Proc.Palaeont. Soc. Japan. K.S.. No. 53, pp. 173-178. pl. 26. Apr. 10, 1964 465. NOTES ON A CRETACEOUS NAUTILOID FROM KYUSHU* TATSURO MATSUMOTO Department of Geology, Kyushu University and MASAHISA AMANO Department of Geology. Kumamoto University 九 州産 の 白亜 紀 お うむ只 類 化 石:鹿 児島 県 痛 子 島 の 白 亜 系 御 所 浦 層 群 中部 層(Grayso- nites漉5を瞳した 部 層 の す ぐ下 位 の三 角 貝 の 多い砂 岩 で,お そ ら く下 部セ マ ニ ア ン)か ら1個 の お うむが い 類 化石 が 褐 られ た 。 これ ばParacymatoceras属 の 新 稀 を 代 表 す る。 本種 は 同属 の模 式種P.asper(欧 州 の チ トニア ン産)と 同 様 に.殻 の 腹面 申 央 に浅 い くぼみ が あ る。 白 亜 紀 のParacymatocerasの 既 知 種 に は こ の くぼみ が な い の に 対 し 注 意 すべ きで あ る 。 縫 合 線 は 波 打 って お り,(Cymatoceras semilobatus(イ ソ ド南部の 上部 ア ル ピア ン)やCenonman- ensis(欧 州 の セ ノマ ニ ア ン)よ りも波 が 強 い 。 本種 がP.asperの 直 系 子孫 か.や や 波 打 った 縫 台 譲 を もつ 部類 のCymatocer訂 邸 の あ る種 類 か ら,側 枝 と して進 化 した も のか は.と くに下 部 白 亜 系産 の もの を今 後 探 求 して よ く比 較 しな い と,断 定 で き な い 。 松 本 逮 郎 ・天 野 昌 久 Introductory Notes awaits a full palaeontological description. Whether Cymaloceras tsukushiense (Ko- Nautilo:ds are rather rare in the Cre- BAVASHI.1954) (em. KUMMEL.,1956). from taceous of Kyushu. YABE, and SIIIMHZU the Tertiary sandstone exposed in the (1924) described Cymatoceras pseudoatlas city of Fukuoka, is a relict or a derived from the middle part of the Senonian fossil is a problem to be settled. Ilimenoura Group, Amakusa, western In this paper we describe an interest- Kyushu. This was represented by a ing specimen of the cymatoceratine nau- single, well preserved specimen. In the tiloid recently obtained from the middle subsequent collection some fragmentary part (Lower Cenomanian) of the Gosho- specimens have been added to it from noura Group of Shishi-jima, Kagoshima the Himenoura Group, but they are in- Prefecture. sufficient for accurate identification. In Before entering into the description, a recent collection from the Albian short remarks are to be given on the Yatsushiro Formation, Kumamoto Pre- stratigraphic occurrence of the specimen fecture, one of us (T. N.) has recognized (see Fig. 1). a small but interesting example of either The stratigraphic sequence of the Go- etninautilus or Paracenoceras, whichII shonoura Group in Shishi-jima has re- Received 7 November 1963; read 10 cently been described by one of us November 1963 at the 86th Meeting of the (AMMAso, 1962, p. 2-4 As in the type Palaeontological Society of Japan. area of Goshonoura island (see MATSU- 173 17-1 Tatsuro MATSUMOTO and Masahisa. AMANO MOTO, 1960, p. 53), the group is divided The nautiloid specimen was obtained into three formations, lower, middle and from the third member, which consists upper. The middle division in Shishi- primarily of fine- to medium-grained jima consists of the following four mem- sandstones, with intercalated dark grey bers in ascending order: siltstone in the upper part. The sand- stone may be occasionally conglomeratic (a) Silty sandstone. about 180 m, with but the conglomerate does not form a Nipponitrigouia. continuous bed. The sandstone is mas- (b) Conglomerate and coarse-sandstone, sive in some parts and well bedded in about 110 m. others. This member is rich in mollusca, (c) Sandstone, about 150 in, rich in tri- gonians. especially in trigonians. The fossils are (d) Siltstone. about 220 m, with Grapso- well accumulated in some parts to form uites. fossiliferous beds and lenticular bodies Fig. 1. Geological sketch map of Shishi-jima (adapted from A\IANO. 1962). 1, II, III: Lower. Middle and Upper Formations of the Goshonoura Group: a-d: Members a-d of the Middle Goshonoura : IV; Himenoura Group (Senonian) : T: Lower Tertiary: •~ : Type locality of Paracrnmtoceras tunghaicum. Inset is a map of Kyushu, indicating the location of Shishi-jima at the center of a small circle and also those of Fukuoka and Kumamoto with F and K. 465. Cretaceous Nautiloid from Kyushu.175 but may be scattered in other parts. Paracymatoceras Iunghaicum sp. nov. The mode of occurrence of the described Pl. 26. figs. la-b: text-figs. 2, 3 nautiloid belongs to the latter category. The fossil was preserved in a massive, olotype:-GK. H6401, an incompletelyH grey, fine to medium-grained sandstone preserved body-chamber and the last which contains Acanthotrigonia pustulosa portion of a phragmocone, in which the (NAGAO). A. ogawai (YEHARA) and .1. test is partly preserved. dilapsa (YEHARA). It is fragmentary Description :-The conch is involute and and in its broken body-chamber small the umbilicus is closed. The body cham- gastropod shells (probably referable to ber is subquadrate in section, slightly Turritella) are embedded. broader than high. The measurements On the evidence of ammonites, Gray- show 61 mm in height and 68 mm in sondes sp. cf. G. founlaini YOUNG, Gray- breadth of the whorl, but the specimen sonites spp. indet, n and )9 (see MATStl- is slightly deformed. The venter is MOTO, 1960), the fourth member is un- broad with a shallow median groove. doubtedly assigned to the Lower Ceno- The flank is gently inflated and abruptly manian. We (AMANO et al. in MATSU- bent at the umbilical shoulder to form MOTO, 1960) have, furthermore, concluded a nearly vertical umbilical wall. The that the Middle Formation of the Gosho- maximum breadth is somewhat below noura Group is wholly referable to the the mid-height. Lower Cenomanian on the grounds of the stratigraphic relation and the contained fossils. Therefore the Sandstone Mem- ber (c), in which the described nautiloid was found. is regarded as a lower part of the Lower Cenomanian. The described specimen is now pre- served in the Type-specimen Room of the Department of Geology, Kyushu Uni- versity, Fukuoka, with register number, GK. H6401. Systematic Description Family Nautilidae D'ORBIGNV, 1840 Subfamily Cymatoceratinae SPATH, 1927 Genus Paracvmatoceras SPATH, 1927 Type-species :-autilus asper (OPPEL) ZITTEL, 1868. Remarks :-This genus, established by SPATH (1927, p. 21), has received good Fig. 2. Paracymatoceras tunghaicum comments by MILLER and HARRIS (1945. sp. nov. Holotype, GK. H6401, natural p. 9) and also by KUMMEL (1956. p. 427% cross section of the body-chamber, •~1. 176 Tatsuro MATSUMOTO and Masahhisa AMAN0 Fig. 3. Paracymatoceras tunghaicun sp. nov. External suture of the holotype, GK. H6401. The ribbing is of cymatoceroid type, species of Paracymatoceras SPATH, 1927. consisting of numerous low ribs which Accordingly it is to be referred to the run almost radially, with slight flexuo- genus Paracymatoceras. sity, on the flank, curved backward on Besides the type-species, which occurs the ventrolateral part and cross the in the Tithonian of Europe, five distinct venter with a strong backward sinus. species and a few indeterminable species forming chevrons. On the internal mould of Paracymatoceras have been known the ribs are impressed on the venter from the Cretaceous of various areas in but the impression is very weak on the the world (see KUMMEL, 1953, 1956). No flank. The ribs are close-set, being ventral groove is observed on all these separated by somewhat narrower inter- hitherto known Cretaceous species, spaces. from which the present species is distin- The suture is sinuous, consisting of a guished. MILLER and HARRIS (1945) broad and low ventral lobe, considerably suggested that those without ventral high, asymmetric, ventrolateral saddle, a groove might be separated from the broad and moderately deep lateral lobe. group of P. asper, but. KUMMEL (1956) a small saddle close to the umbilicus holds that the genus Paracymatoceras is and a shallow and small umbilical lobe. variable in this respect. Anyhow it is The internal suture is not clearly ex- interesting to note that the present posed. The siphuncle crosses the septum species represents a Cretaceous example at a point somewhat dorsad from the of the group of P. asper with a ventral center. groove. Remarks:-lthough a single, imper- The suture of the present species is fectly preserved specimen is at our not quite identical with that of P. asper. disposal, the observed characters are so In the latter species there is no ventral distinctive that the establishment of a lobe and the dorsolateral saddle is larger new species is justifiable as discussed and more distant from the umbilicus below. than in the present species. Comparison :-In the sinuous suture, Among the Cretaceous species, Paracy- subquadrate whorl section with a ventral matoceras texanum (SHUMARD) (1860, p. groove and cymatoceroid ribbing this 50), from the Washita Group of Texas, species is generally allied to Paracymato- as described by MILLER and HARRIS ceras asper (OPPEL) (ZITTEL, 1868. p. 48, (1945, p. 10, pl. 3, figs. 1, 2 ; pl. 5, figs. p1. 3, fig. 1 ; MILLER and HARRIS. 1915, 1-3 ; text-fig. 3) has deeper lateral lobe p. 9, pl. figs. 1-3 ; KUMMIEL,1956, p. 427, than the present species and no ventral text-fig. 23G, pl. 19, figs. 1, 2), the type- lobe. It has a much more compressed 4165. Cretaceous Nautiloid from Kyushu 177 conch than the present species. represents a new species of Paracymato- As KUMMEL (1956) has pointed out. ceras, named P. tungbaicum. It has a certain species of Cymatoceras HYATT, shallow groove along the mid-ventral line 1881, have fairly sinuous sutures, being like P.