Cryptopecten kyushuensis (Nagao, 1928)
NAGAO, T. 1928. Paleogene Fossils of the Islands of Kyushu, Japan. Part 2. The Science Reports of the Tōhoku University [2nd. Series -Geology], 12 (1): 11-140, pls. 1-17. [p. 37, pl. 8, figs. 1,1a]
1928 Pecten kyushuensis Nagao, 1928
T. Nagao, 1928, plate 8.
|
«Right valve [?] small, about 20 mm. high, regularly convex, nearly equal in height and length; equilateral except for the ears; ears broken at the ends, but probably trigonal, the posterior one slightly larger, with its outer margin almost vertical; umbo pointed, with an angle of about 110° subtended by the two dorsal margins; antero- and postero-dorsal margins nearly equal in inclination and almost straight, and the ventral one partly broken, but perhaps broadly rounded judging from the lines of growth. Surface ornamented with radial ribs and grooves in alternation; ribs about 19 in number, equal in width to one another, well rounded on top, elevated and straight; grooves deep, flattened at the bottom, and much narrower than the ribs themselves; both ribs and grooves corroded, but with a trace of fine imbrications.
There is here a single imperfect specimen of Pecten, the subgeneric position of which is not definitely determined because of the only partial preservation of the ears. Although the present specimen is imperfect, it is easily distinguished from all the species which have been recorded from the Japanese Recent and Neogene. P. (P.) dickersoni WAGNER and SHILLING¹ from the Oligocene of California, is somewhat akin to ours, but has less numerous, rail-shaped and sometimes longitudinally grooved radial ribs, and larger cars. Locality and geological horizon: The Wakita Beds; Wakita, Shimago-mura, Onga-gun, province of Chikuzen.» ¹ C. M. WAGNER and K. H. SHILLING: "San Lorenzo Group of the San Emigdio Region, California." Univ. Calif. Publ., Geol., Vol. XIV. p. 253, Pl. XLV, fig 1.
TAKUMI NAGAO, 1928
|
«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.
|