Mizuhopecten matumoriensis (Nakamura, 1940)
NAKAMURA, M. 1940. On some Pectinidae fossils from the Miocene deposits of the Tomiya Block, Miyagi-ken, Northeast Honsyû, Japan. Japanese Journal of Geology and Geography, 17 (1-2): 1-15, pIs. 1-2 [p. 13, pl. 1, figs. 1-2; pl. 2, figs. 1-3]
1940 Pecten (Patinopecten) kimurai matumoriensis Nakamura, 1940
M. Nakamura, 1940, plates 1, 2.
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«Shell large in size, circular in outline, much compressed. Valves sculptured by 10-12 strong, radial ribs, which are rather sharply elevated, round on top and nearly equal to or a little narrower than its interspaces. Interspaces smooth on both bottom and sides; otherwise similar to P. kimurai. Length 146.5 mm., width 145.2 mm., depth of intact valves 34.5 mm.
This subspecies is distinguishable from the species particularly by having a greater number of radial ribs which are not only stronger and more crowded, but also show different growth in the immature stage. In the young, the ribs resemble somewhat those of Pecten yessoensis JAY, yet differ considerably upon continued growth of the shell. The gently raised, sharply rounded, more crowded and greater number of ribs serve to distinguish this subspecies from both P. kimurai and P. kimurai tiganouraensis n. subsp. Locality:— Matumori, Nanakita-mura, Miyagi-gun. Horizon:— Nanakita beds.» MANZIRÔ NAKAMURA, 1940
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