Mizuhopecten kimurai kagaensis Ogasawara, 1976
OGASAWARA, K. 1976. Miocene Mollusca from Ishikawa-Toyama Area, Japan. Science Reports of the Tohoku University [2nd. Series - Geology], 46 (2): 33-78, pls. 11-15. [p. 43, pl. 14, figs. 10, 17; pl. 15, figs. 8, 9, 12, 16, 18]
1976 Mizuhopecten kimurai kagaensis Ogasawara, 1976
K. Ogasawara, 1976,
plates 14, 15. |
«Description: — Shell large, modelately thick, inflated, orbicular and subequilateral except for auricles. Some specimens exceed 100 mm in length and height. Surface of right valve sculptured with about 10, low, round-topped radial ribs and fine concentric lines. Radial ribs wider than their interspaces and divided into seven or eight riblets which are distinct especially on both extremities and ventral margin, but indistinct on the umbonal area. Radial ribs on the both discs low and weak. Rather flat left valve sculptured with narrowly elevated radial ribs and fine concentric growth lines. Their interspaces covered by fine decussate sculpture. Profile of radial ribs rather sharp near their beaks, and becomes weak and round towards ventral margin. Interspaces on the both extremities sometimes sculptured with few longitudinal riblets. Both auricles nearly equal in size, and sculptured with five to seven, faint radial threads and fine concentric lines. Byssal notch rather wide but shallow. Hinge line straight with simple cardinal crura. Resilial pit small, wide and shallow with shallow lateral ridge. Interior surface gently folded according to external ribs. Impression of muscle scars indistinct.
Measurenments: Remarks: — This new subspecies resembles Mizuhopecten kimurai murayamai (Yokoyama, 1926), but the former differs from the latter by having about 10, low flat-topped radial ribs and wide apical angle (about 110-120º). Mizuhopecten kimurai nakosoensis closely resembles the present subspecies, but is distinguishable from the latter by having distinct and much number of riblets at the both extremities of shell.
The present subspecies is also characterized by shouldered dorsal margins among the kimurai group. Locality and Formation: — River floor of Sai-kawa, about 1000 m upstream, Omma Bridge, Omma, Kanazawa City, Ishikawa Prefecture. Saikawa Formation.» KENSHIRO OGASAWARA, 1976
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