Mizuhopecten yessoensis nakatonbetsuensis (Masuda, 1962)
MASUDA, K. 1962. Tertiary Pectinidae of Japan. Science Reports of the Tohoku University [2nd. Series - Geology], 33(2): 117-238 [p. 214, pl. 24, fig. 4]
1962 Patinopecten yessoensis nakatonbetsuensis Masuda 1962
K. Masuda 1962, plate 24.
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«Holotype: — DGS, Reg. No. 3899. A single left valve.
Description:— Shell moderately thick, suborbicular, slightly inflated; valve radiately ribbed, apical angle about 100º. Valve with about 28, distinct, round-topped radial ribs, a few, round-topped intercalary threads, concentric growth lines and distinct network; radial ribs subequal to their interspaces in breadth, sometimes with a single or a few intercalary threads in which one in central part of disc appears near beak; auricles moderate in size; anterior larger than posterior with several, distinct radial threads and distinct concentric lines by which they appear imbricated; posterior one truncated behind at obtuse angle; interior surface unknown. Dimensions (in mm.):— Height 100, length 104, hinge-length 45.5, depth ca. 7. Comparison and Affinity: — The present subspecies resembles yessoensis (s. s.), but it has rather elevated, broad radial ribs, intercalary threads and the auricles sculptured with distinct, imbricated radial threads and distinct concentric lines. Remarks: — The characters of the right valve remain unknown. Type locality, Geological formation and Age: — Asahidai, Nakatonbetsu-machi, Esashi-gun, Kitami Province, Hokkaido (Lat. 45°N., Long. 142°18'E.). Nakatonbetsu formation. Late Miocene. Distribution: — Known only from the type locality.» KÔICHIRÔ MASUDA, 1962
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