Spondylus pseudocalcaratus Tashiro, 1976
TASHIRO, M. 1976. Bivalve faunas of the Cretaceous Himenoura Group in Kyushu. Paleontological Society of Japan, Special Papers, 19: 102 p., pls. 1-12, text-figs. 1-23. [p. 54, pl. 5, figs. 1-9, text-fig. 19]
1976 Spondylus pseudocalcaratus Tashiro, 1976
M. Tashiro, 1976, plate 5.
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«1954. Spondylus sp. MATSUMOTO, The Cretaceous System in the Japanese Islands, Tokyo, p. 152.
Material:— Holotype, KE 2115, from loc. 47; paratypes, KE 2117-20, from the same locality; paratype, KE 2116, from loc. A1.
Description:— Shell medium to large, inequivalve, roundly ovate, a little higher than long; umbo situated at a little anteriorly from the center; left valve less convex and thinner than right valve; hinge margin straight about a half length of valve; anterior margin weakly arched; ventral margin well rounded; posterior margin nearly straight; apical angle of left valve about 85°; both ears triangular; posterior ear slightly larger than anterior one; surface of right valve ornamented with about 6 irregular and well laminated concentric ribs and about 8 weak radial ribs; surface of left valve ornamented with numerous radial ribs which consist of about 8 primary, 5 or more secondary and about 30 tertiary ribs; primary ribs strong, with several spines on them; secondary ribs appear from a part about a half of height, with several spines; these spines well developed on the ribs of posterior half of the disk; ligament area of right valve wide, triangular, with a deep ligament groove; about 15 horizontal striae and a few chevron-shaped striae on the ligament area; inner margin crenulated by radial ribs.
Remarks:— The spines on primary ribs are usually about 7 but sometimes 10 in number. The secondary ribs are invisible in the young stages of some specimens. In the immature stages, the outline of the valve is generally subquadrate and spines are a few or sometimes effaced.
Spondylus japonica AMANO and MARUI (1958) from the Ukiyama Formation of Nagano Prefecture is closely similar to this species in having spinose radial ribs of left valve and strong concentric ribs of right valve. S. japonicus has however, a taller valve than this species and no secondary ribs. Spondylus calcaratus FORBES (STOLICZKA, 1871) from the Trichinopoly Group of India resembles this species in the radial ribbing of left valve, but differs in having more irregular and concentric ribs of right valve. Spondylus gregalis MORTON (WHITFIELD, 1885) from the Green marls of New Jersey is distinguishable from this species by less numerous radial ribs of left valve. Spondylus decoratus NAGAO (1934) from the Miyako Group of Iwate Prefecture differs from this species in having a different general outline, less spinose secondary ribs, and weaker concentric ribs of the right valve. Occurrence:— Locs. A1, A7, K1?, U3; Formation L-I; Upper Urakawan (Santonian).» MASAYUKI TASHIRO, 1976
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