Decatopecten tayamai (Nomura & Niino, 1932)
NOMURA, S. & H. NIINO. 1932. Fossil Mollusca from Izu and Hakone. Science Reports of the Tohoku University [2nd. Series - Geology], 15(3): 169-192. [p. 178, pl. 11, figs. 6-8]
1932 Pecten (Decadopecten) tayamai Nomura & Niino, 1932
S. Nomura & H. Niino, 1932,
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«Shell attains about 60 mm. in height, much higher than long, compressed, almost equivalve, subequilateral; sides sloping, long and straight; base regularly rounded, umbonal angle about 60°; test rather solid. Right valve with 14 prominent, rounded and subequal ribs, accompanying a single riblet on each side of disk; interspaces rounded at base and nearly equal to ribs; whole surface covered with numerous radial riblets (about 7 or 8 on each rib), crossed by fine, more or less imbricating lines of growth. Ears small; much shorter than half the disk length; posterior ear a little larger than the anterior, almost rectangularly truncated, the anterior with a wide and shallow notch below; both ears similarly sculptured by about 5 radial riblets as well as fine concentric lines. Left valve similar in every respect to the right except for subequal ears.
Dimensions:— Height, 55 mm.; length, 41 mm.; depth, ca. 7 mm.; length of hinge, 18 mm. (a right valve). There is a specimen larger than that measured, and unfortunately fractured at its umbonal part. No allied forms have hitherto been reported in Japan either recent or fossil. Occurrence:— Nagata in Shirahama-mura, ? Ichiyama near Yugashima (Shirahama Group).» SHICHIHEI NOMURA & HIROSHI NIINO, 1932
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«Among the species of Mizuhopecten described from Neogene formations in the Japanese Islands, Mizuhopecten planicostulatus (Nomura and Niino, 1932), described from the Pliocene Shirahama Formation, Izu Peninsula, Shizuoka Prefecture, Central Japan, is of particular interest because of its very restricted geologic range and geographical distribution in association with some very characteristic molluscs such as Amussiopecten praesignis (Yokoyama), Chlamys satoi (Yokoyama), Chlamys shirahamaensis (Nomura and Niino), Comptopallium tayamai (Nomura and Niino), Perotrochus yabei (Nomura and Niino), Strombus luhuanus Linnaeus, etc. Among these, Amussiopecten praesignis and Chlamys satoi are representatives of the Kakegawa fauna that is distributed in the southern part of the Japanese Islands.
Comptopallium tayamai (Nomura and Niino) is of particular interest because of its peculiar morphology and it can be distinguished from other pectinids by its weakly inflated, oblique, higher shell which has about 17 stout radial ribs with numerous, fine radial threads, and by its nearly equal-sized triangular auricles with wide and shallow byssal notch. From the accounts given above, it is interesting to note that the molluscan fauna of the Shirahama Formation can be referred to the Kakegawa fauna based upon the presence of the Amussiopecten praesignis assemblage (Masuda and Ogasawara, 1981). However, Mizuhopecten planicostulatus is known from the Shirahama Formation in the environs of the Izu Peninsula and from the Kurotaki Formation of the Boso Peninsula, Chiba Prefecture, and its distribution forms a remarkable contrast with that of Mizuhopecten tokyoensis hokurikuensis, (Akiyama) known from Pliocene formations distributed from Taiwan to Hokkaido (Fig. 4). Comptopallium tayamai is known only from the Shirahama Formation.» MASUDA, K. 1986. Notes on the origin and migration of Cenozoic pectinids in the Northern Pacific. Paleontological Society of Japan, Special Papers, 29: 95-110, pls. 7-10. In T. Kotaka (Ed.), Japanesse Cenozoic mollusca: their origin and migration, vii, 255 p., pls. 1-21. [p. 103]
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Comptopallium tayamai (Nomura and Niino); K. Masuda, 1986, Notes on the origin and migration of Cenozoic pectinids in the Northern Pacific, pl. 10, figs. 5, 6.
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