Chlamys tamurae Masuda & Sawada, 1961
MASUDA, K. & Y. SAWADA. 1961. Some new Tertiary
pectinids from Southwestern Hokkaido, Japan. Japanese Journal of Geology and
Geography, 32 (1): 19-29. [p. 27, pl. 4, figs. 12-15]
1961 Chlamys tamurae Masuda & Sawada, 1961
K. Masuda & Y. Sawada, 1961,
plate 4. |
«Description:— Shell rather thin, higher than long, moderately inflated, subequivalve; inequilateral, length of posterior side longer than that of anterior side; both valves radiately ribbed and forming an angle of about 80° at apex. Right valve moderately inflated, with numerous, rather distinct, close-set, densely scaled, fine radial ribs, finely scaled, fine intercalary threads, fine concentric growth lines and obtuse network; radial ribs usually narrower than their interspaces; interspaces between radial ribs with intercalary threads in which primary ones appear near beak and secondary ones at about half of disc; intercalary threads nearly equal to radial ribs in strength near ventral margin; posterior submargin sculptured with finely scaled, fine radial threads continuing to posterior auricle; whole surface more or less folded; auricles moderate in size; anterior auricle much larger than posterior furnished with narrow and deep byssal notch and wide byssal area, sculptured with several, distinct, finely scaled radial threads which are narrower than their interspaces and fine concentric lines; posterior one sculptured with several, finely scaled, fine radial threads, intercalary threads and fine concentric lines; hinge with rather distinct, simple cardinal crura, rather wide and deep resilial pit with distinct, short lateral ridges and prominent ctenolium. Left valve moderately inflated, with sculpture nearly similar to right valve except for several, more or less distinct foldings on whole surface; raised part broader than their valleys; radial ribs and intercalary threads on crests more densely scaled and more or less broader than their interspaces, but those in valleys narrower than their interspaces; anterior auricle sculptured with several, rather distinct, finely scaled radial threads, intercalary threads and concentric lines; posterior auricle with finely scaled, fine radial threads and concentric lines. Interior surface of both valves smooth but with fine marginal serration.
Dimensions (in mm.):-- Comparison and Affinity:— The present species is related to Chlamys opuntia (DALL) (1898, p.707, pl. 29, fig. 6) but it is distinguishable therefrom by the more or less posteriorly contorted shell, the undivided radial ribs which are usually narrower than their interspaces, somewhat folded surface and regularly inflated valve. Also Chlamys mollita (REEVE) (1853, sp. 100) somewhat resembles the present one but it is distinguishable by its suborbicular and equilateral shell, larger apical angle and unfolded surface.
Remarks:-- The present species is named in honor of Mr. Yoshiharu TAMURA of the Institute of Geology and Paleontology, Tohoku University, who assisted the writers in collecting the specimens. This species is characterized by its small, rather thin, moderately inflated shell, numerous, densely scaled, close-set radial ribs and intercalary threads in the right valve and by the left valve having several, more or less distinct foldings on whole surface. The shell convexity of the present species is asymmetrical, the maximum depth being situated posteriorly in the right valve and anteriorly in the left valve. Type locality, Geological formation and Age:-- Small hill-side exposure at Maruyama, Kita-Hiyama-machi, Setana-gun, Shiribeshi Province, Hokkaido (Lat. 40°23'56''N., Long. 139°54'55''E.). Setana formation. Pliocene. Distribution:-- Known only from the type locality. Occurrence:-- Abundant in the calcareous medium-grained sandstone.» KÔICHIRÔ MASUDA & YOSHIO SAWADA, 1961
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