Cryptopecten hataii (Kanno, 1958)
KANNO, S. 1958. New Tertiary Mollusca from the Chichibu Basin, Saitama Prefecture, Central Japan. Science Reports of the Tokyo Kyoiku Daigaku [Section C -Geology, Mineralogy and Geography], 6 (55), p. 157-229, pls. 1-7. [p. 169, pl. 1, figs. 14-18]
1958 Aequipecten hataii Kanno, 1958
S. Kanno, 1958, plate 1.
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«Shell small, rather thin, slightly convex, subcircular to longitudinally ovate in outline, subequivalve, equilateral except for auricles, Surface with radial ribs crossed by faint concentric lines of growth. Right valve with about 17 radials of almost uniform, simple low rounded, flat-topped ribs separated by shallow valleys of equal or more or less narrow, smooth interspaces; some ribs with obsolete sulci on their summits. Hinge-line oblique and straight, almost more than one-half hell length; anterior auricle much larger and longer than the posterior, with fine, close, concentric sculpture and 5 -6 distinct fine imbricated radials; notch rather conspicuous, ctenolium distinct; posterior auricle sculptured similarly as anterior; interior surface reflacting the external ribs. Left valve with microscopic cross-hatching network on the umbonal area, and with about 17 radial ribs of uniform size excepting marginal ones, which are simple, rather distinct, narrowly rounded, separated by shaJlow valleys of wider interspaces, provided with 2-3 obsolete radial striae extending to half shell length; anterior auricle a little larger than the posterior and sculptured with 5-6 imbricated radials and concentric lines; inner surface not obvious.
Measurement (in mm.): Comparison:— This new species is similar to Chlamys notoensis (YOKOYAMA) (YOKOYAMA, 1929, pp. 4-5, pI. 3, fig. 4; pI. 5, figs. 1--2) with respect to the bifurcating and few number of radial ribs, but the equal, large number of radial ribs and the lack of intercalary ones serve to distinguish it from that species. Pecten kyushuensis NAGAO (NAGAO, 1928, p. 37, pI. 8, figs. 1, 1a) from the Oligocene of North Kyushu, Japan, is somewhat akin to the present one, but has numerous, simple, well rounded, elevated, radial ribs. Aequipecten perplanus (MORTON), 1833, (TUCKER-ROWLAND, 1938, pp. 29-30, pI. 6, fig. 12), from the Jackson Eocene and Vicksburg Oligocene in North America, is another related species to the present one, but the former differs from the latter by having a large number of radial ribs (20-25), and two parallel sulci on the ribs which measure about 10 mm. from the ventral margin on adult valves, and by the scaly ornamentation on the surface.
Remarks:— Many specimens were examined. Of the present specimens the rounded form may be the natural form because of the elongate form (higher form) have greater thickness, smaller apical angle, and narrower interspaces of the radial ribs than those of the rounded forms. It is very interesting that the present species closely resembles the American Paleogene species of Aequipecten, and such similarity may have relation with specific origin of the group. The specific name is dedicated to Prof. Kotora HATAI of the Geological Institute, Faculty of Education, Tohoku University. Locality and geological formation:— Loc. 205, a small road side exposure, about 600 meters west of Chigaya mineral spring, Chigaya, Yoshida-machi. Reg. Nos. 5616. holotype, 5617, paratype. Nenokami sandstone (bluish grey, fine-grained sandstone), Upper Oligocene. Associated fauna:— Venericardia tokunagai YOKOYAMA, Macoma arctata (CONRAD), M. snohomishensis WEAVER, M. sookensis CLARK and ARNOL., Mya grewingki MAKIYAMA, Panomya elongata KANNO, n. sp., Cultellus otukai OGASAWARA and TANAI, Crepidula auricula YOK., Neptunea araii KANNO, n. sp. Geographic distribution:— Known only from the present area. Geological range:— Upper Oligocene.» SABURO KANNO, 1958
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«Two Early Miocene (formerly regarded as Late Oligocene) species, Pecten kyushuensis Nagao, 1928, from the Waita Formation in Fukuoka Prefecture (north Kyushu) and Aequipecten hataii Kanno, 1958, from the Nenokami Formation in Saitama Prefecture (central Honshu), are possibly early representatives of Cryptopecten, but their phylogenetic relation to Middle Miocene and later species is by no means certain owing to the poorly preserved nature of the material.»
HAYAMI, I. 1984. Natural history and evolution of Cryptopecten (A Cenozoic-Recent Pectinid Genus). The University Museum, The University of Tokyo, Bulletin, 24: 1-149, pls. 1-13.
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