Chlamys imanishii 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, pl. 4. [p. 25, pl. 4, figs. 10a-c, 11]
1961 Chlamys imanishii Masuda & Sawada, 1961
K. Masuda & Y. Sawada, 1961,
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«Description:— Shell moderate in size, thickness and convexity, somewhat higher than long, subequilateral except for auricles, subequivalve; valves radiately ribbed and forming an angle of about 85° at apex. Right valve with about 25 or a little more, round-topped but somewhat imbricated, fine radial ribs, scaled, fine intercalary threads, fine concentric growth lines and distinct fine network; radial ribs narrower than their interspaces, divide into two or rarely three parts by rather deep longitudinal furrows on lower part of disc towards ventral margin but radial ribs near submargins usually remain undivided; intercalary threads usually appear on upper part of disc, rarely divide into two parts near ventral margin, subequal to divided radial threads in strength at ventral margin; submargins with very fine imbricated radial threads; auricles moderate in size; anterior auricle larger than posterior, furnished with prominent byssal notch and wide byssal area, rvith several, imbricated, fine radial threads and concentric lines; posterior one truncated behind at obtuse angle, similar to anterior in sculpture; hinge with conspicuous cardinal crura, wide and deep resilial pit with distinct lateral ridges and prominent ctenolium. Left valve with sculpture nearly similar to right valve, though imbrications on radial ribs and intercalary threads are more prominent. Interior surface rather smooth but with fine marginal serration.
Dimensions (in mm.):-- Comparison and Affinity:-- Chlamys islandica hindsii (CARPENTER) (Op. cit.) resembles the present species but it is distinguishable by its rather large
shell, rather prominent, flattish radial ribs which are broader than their interspaces, finer intercalary threads which appear at lower parl of disc of the right valve and by the left valve having finely scaled, elevated radial ribs and prominent, larger number of finely scaled intercalary threads. Chlamys tamurae described in the present article, also resembles the present one but differs by its posteriorly contorted shell and larger number of finelly scaled radial ribs and intercalary threads. Remarks:-- The present species is named in honor of Mr. Shigeru IMANISHI of the Geological Institute of Kumamoto University, who collected the holotype specimen from the Hamada formation in Aomori Prefecture. This species is characterized by its small shell, about 25, finely scaled, rather low, fine radial ribs, finely scaled intercalary threads, distinct network on surface, conspicuous cardinal crura, prominent ctenolium in the right valve and by the left valve having the nearly similar sculpture with the right valve. Type locality, Geological formation and Age:-- Sea cliff at Hamada, Yokohamamura, Kami-Kita-gun, Aomori Prefecture (Lat.41°08'15''N., Long. 111°16'34''E.). Hamada formation. Early Pliocene. Distribution:— Hamada formation, Aomori Prefecture and Setana formation, Hokkaido: both Early Pliocene in age. Occurrence:— Few in the calcareous medium-grained sandstone of the Hamada formation; rare in the calcareous coarse-grained sandstone of the Setana formation.» KÔICHIRÔ MASUDA & YOSHIO SAWADA, 1961
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