Mizuhopecten subyessoensis (Yokoyama, 1930)
YOKOYAMA, M. 1930. Tertiary Mollusca from south Karafto. Journal of the Faculty of Science, Imperial University of Tokyo, Section II, Vol. 2 (10): 407-418 [p. 416, pl. 80, figs. 3, 4]
1930 Pecten subyessoensis Yokoyama, 1930
M. Yokoyama, 1930, plate 80.
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«Shell medium-sized, inequivalve, almost equilateral, circular. Right valve moderately convex, with about twelve broad flattened radiating ribs separated by somewbat narrower interstices. Left valve flat, with about nine rounded radiating ribs which are narrower than interstices; ears almost equal, triangular.
The specimens are few and imperfect, a single right valve which we possess lacking the ears. I at first took them for Pecten yessoensis Jay of our northern seas to which they show a striking resemblance save for the lIumber of ribs which in the latter number more than eighteen and up to twenty-four. Fossil occurrence. — Naikawa Beds of the Nairo-Naikawa Coalfield: Sakikawa, Haushigawa and Kaisawa, all three in Tomarigeshi-mura, Shiska-gun; Isos, Higashi-Sakutan, Motodomari-gun.» MATAJIRO YOKOYAMA, 1930
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