Cryptopecten oyamadensis Hirayama, 1954
HIRAYAMA, K. 1954. Miocene Mollusca from the Arakawa Group, Tochigi Prefecture, Japan. (Part 1). Science Reports of the TokyoKyoiku Daigaku [Section C - Geology, Mineralogy and Geography], 3 (18): 43-75, pls. 3-5. [p. 54, pl. 3, fig. 3]
«Cryptopecten oyamadensis HIRAYAMA, n. sp.
Pl. III, Fig. 3. Shell rather small, measuring 28.2 mm in height, 4.5 mm in convexity of left valve and 28.0 mm in approximately length. Shell higher than long, elongated subrounded in shape, moderately convex, the convexity greatest umbonalIy, apical angle 102°, sides sharply descending then curving into antero-ventral side. Surface provided with nine radial riblets, which at their umbonal region bifurcate and soon extend ventrally as separate riblets, on the whole crossed by fine meshwork. Radial ribs at central to ventral margin rounded, but provided on their backs with minor radial striae which are about equal to their interspaces; major ribs narrower than their round bottomed interspaces which also have fine radial striae. Radials at posterior part of the shell sharper than those of anterior part. Anterior ear with several rough riblets.
Remarks. — Although not preserved perfectly, this new species is characterized by its few number of radials which spilit at an early stage, the swollen umbonal region and by both the radial ribs and interspaces having fine radial striae, both of which are covered with fine meshwork. No species similar to the present one has been dsecribed from the Cenozoic deposits of Japan. This species is distinguishable from the genotype of Cryptopecten, C. alli DALL, BARTSCH and RHEDER (1938, p. 93, pI. 23, figs. 1-4, 7), a Recent shell from the Hawaian Islands by the fewer number of radial ribs and narrower shell outline. Locality and horizon. — Loc. 3, A small valley of Shimogo, Oyamada-mura. Lat. 36°46'40'' N, Long. 140°12'45'' E. Rare. Kobana formation, Miocene. Reg. No. 10112. (Holotype)» KATSUMI HIRAYAMA, 1954
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K. Hirayama, 1954, plate 3.
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