Eopecten maizurensis Nakazawa, 1952
NAKAZAWA, K. 1952. A study on the pelecypod-fauna of the Upper Triassic Nabae group in the northern part of Kyoto Prefecture, Japan. Part 1. Pectinids and limids. Memoirs of the College of Sience, University of Kyoto [Serie B], 20 (2): 95-106, pls. 7-10 [p. 97, pl. 7, figs. 3-6]
1952 Velata maizurensis Nakazawa, 1952
K. Nakazawa, 1952, plate 7.
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«1952 Chlamys sp. indet. Kobayashi and Ichikawa, p. 78, pl. 3, fig. 14.
Description: – As all specimens are considerably deformed; accurate descriptions of their outlines cannot be given.
Shell fairly large, remarkably inequivalve, inequilateral, obliquely oval, hingeline straight, antero-dorsal margin slightly concave and longer than linear postero-dorsal; ventral margin rounded, but abruptly rising up backward, and antero-ventraly projected. Right valve almost flat, posterior ear even and small, obtusely triangular, anterior ear larger than posterior one, sinuated deeply below as in Chlamys. Surface ornamented with many weak riblets, which, in paratype (Pl. VII Fig. 5), are very fine and separated by flat smooth interstices at the umbo, and some 5 mm. from the umbo, secondaries appear as strong as primaries, both increasing to more than 60 in number; in advanced growth they are gradually enlarged to the size of interspaces; on the anterior ear about 7 radial ribs and on the posterior ear 3 weak radials are present. Left valve gently convex, umbo slightly projected over hinge-margin, both ears obtusely triangular, distinctly depressed, anterior ear larger. Surface sculptured by radial ribs of three or four orders i.e. primaries, secondaries, tertiaries and quaternaries. On the umbo of another paratype only 17 primaries (Pl. VII Fig. 6) are visible, while some 6 mm below the umbo secondaries appear alternating with primaries, and approximately 10-20 mm apart from the umbo, the tertiaries are inserted; near the peripheral margin quarternary riblets appear in various places. The ribs are faint and separated by flat wide interstices till the tertiaries make their appearance, but gradually grow larger and intersticles become narrower to form mere boundary sulci; in the full grown stage tertiaries enlarge to the size of secondaries, and 3 or 4 irregularly graded riblets being visible between strong primaries on the peripheral zone. Both valves are covered with fine crowded concentric growth-lines, which become stronger on the ears and peripheral margin and cross the radials to make reticulate or slightly knotted appearance. Dimensions:
Remarks and comparison: – The specimens are deformed and elongated anteroposteriorly; they are understood to differ considerably from original shapes. Perhaps the apical angle is narrower, the height being nearly equal to or greater than the Iength, and the anterior ear of the left valve nearly rectangled triangular. This species bears a close resemblance to those of Chlamys and its right valve can hardly be distinguished from that of Chlamys mojsisovicsi Kob. and Ichi., but judging from the remarkable unequalness of both valves — the considerable dfference of their sculpture, the flatness of the rlght valve — and the differentiated ornamentation of the left valve, this species may be more suitably classified under Velata. But this species has smaller anterior ear more distinctly bordered from the disk, and straighter ribs than the typical species of Velata.
Chlamys sp. indet. Kob. & Ich. 1952 from Heki was described to have a well developed anterior wing of Chlamys type, but after careful observation of the original specimen the writer has recognized that its wing as well as its umbo are destructed and seperated from the main part of the shell by secondary external forces, and in consequence the wing seems to have a deep byssal sinus. This specimen is nothing else but the right valve of Velata veszprimiensis, as complemented by Ichikawa in their postscript. (Kobayashi and Ichikawa, 1952, p. 84) The ornamentation of the left valve reminds one of those of Carnic Velata veszprimiensis (Bittner), V. venestula (Bittn) from Bakony (Bittner, 1901) and Jurassic V. velata (Goldfuss) (Goldf, 1833, p. 45, Pl. XC, fig. 2.) but the ribs are less in number than veszprimiensis and velata, and more numerous than venestula. The most characteristic fearure is the antero-ventrally elongated ovate outline of the shell as that of Lima, but whether this is caused only by deformation or not is a problem yet to be solved. Occurrence: – N2 bed and lower part of N4 bed and uppermost part of lower bed of Heki formation. Kongoin (Loc. No. N-102, 103), Miuchi (N-414), Shinmichi (N-405), Sugitani (N-503). Omachi (N-504), Monobe (N-601), Heki (N-701), (Reg. No. JM 100 22-10026)» KEIJI NAKAZAWA, 1952
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