Nanaochlamys Hatai & Masuda, 1953
HATAI, K. & K. MASUDA. 1053. On the Pecten notoensis (Yokoyama). (On the Miocene Pectinidae from the environs of Sendai, Part 2). Transactions and Proceedings of the Palaeontological Society of Japan [N. S.], 11: 75-82, pl. 7, text-figs. 1-3. [p. 76]
«Genus Nanaochlamys HATAI and MASUDA, n. gen.
Genotype:— Pecten notoensis YOKOYAMA, 1929.
Type locality:— Calcareous sandstone of the Miocene Nanao formation at Iwaya, Nanao City, Ishikawa Prefecture. Geological range:— Early Miocene.
Diagnosis:— Equilateral, subequivalve, suborbicular, thick-shelled, moderately inflated; five to six, smooth or rarely nodulose ribs, which bifurcate at or near anterior margin and carry several intercalary threads. Auricles unequal, the anterior larger and with strong radial threads and fine concentric lines, the posterior with radial threads and fine concentric lines. Byssal notch conspicuous. Ctenolium rarely ill-developed. Valves unequally convex, the maximum points of convexity situated at different distances from the beak.
Remarks:— Pecten notoensis has been referred to the genus Chlamys because of its Chlamys-like aspect, but it is distinguished from that genus by the well developed byssal notch and ctenolium, pronounced imbricated surface, and by the surface of the valves being similarly sculptured with radial ribs. This new genus resembles Mesopeplum lREDALE (IREDALE 1929, pp. 162-164), from the depth of 40-80 fathoms off New South Wales, Eastern Australia. The latter, however, has five prominent, distant, compound ribs, with the intervals broader than the ribs, three riblets on the back of the ribs and four to eight, fine riblets in the interspaces between the ribs on the left valve; similarly the right valve has five compound ribs whose intervals are narrower than broad, and bear four to eight riblets on their back and two or three rib lets in the interspaces; and the byssal notch is minute and hardly noticeable. Therefore, the latter is easily distinguished from the former by the characters of the ribs, difference in sculpture of the right and left valves and by the conspicuous byssal notch. The genus Scaeochlamys (IREDALE 1929, pp. 162-163) resembles Nanaochlamys in having discrepant sculpture of the right and left valves, but is distinguishable from the latter by the pronounced byssal notch and pectinidial teeth, few prominent scaly ribs on the left valve and numerous less scaled ribs on the right valve.»
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Pecten notoensis Yokoyama; M. Yokoyama, 1929, Pliocene Shells from near Nanao, Noto, plate 3, figures 1-4.
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KOTORA HATAI & KÔICHIRÔ MASUDA, 1953