Chlamys akutsui Masuda, 1962
MASUDA, K. 1962. Tertiary Pectinidae of Japan. Science Reports of the Tohoku University [2nd Series - Geology], 33 (2): 117-238, pls. 18-27. [p. 160, pl. 18, fig. 29]
1962 Chlamys akutsui Masuda, 1962
K. Masuda, 1962, plate 18.
|
«Holotype: IGPS*, colI. cat. no. 28293; a single left valve.
Description:– Shell moderate in size and thickness, moderately inflated, higher than long,subequilateral except for auricles; valve radiately ribbed, pointed at top and forming anangle of about 85° at apex. Valve with ten, strongly elevated, round-topped radial ribs and intercalary threads; radial ribs narrower than their interspaces; radials near submargins much lower than those of central part of disc, usually divide into two or three, nearly equal riblets at upper part of disc towards ventral margin; interspaces between radial ribs roundbottomed, with rather fine intercalary threads which usually appear on lower part of disc; intercalary threads near submargins usually appear near beak, subequal to divided riblets at ventral margin; auricles moderate in size; anterior auricle larger than posterior, with wide and shallow, distinct byssal sinus, sculptured with several, fine radial threads and concentric lines; hinge with rather indistinct cardinal crura, narrow and rather deep resilial pit provided with shallow lateral sockets. Interior surface distinctly folded. Dimensions (in mm.):– Height 41, length 37, hing-Iength ca. 17, depth 9.8. Comparison and Affinity:– This species more or less resembles the water worn specimens of Gloripallium crassivenium (Yokoyama), but differs by its inflated shell, strongly elevated, round-topped radial ribs and fine intercalary threads. Remarks:– Since the description is based upon a single left valve, the characters of the right valve remain unknown. The specimen probably referable to the present one from the Miocene Tamatsukuri formation in Shimane Prefecture, is ornamented by rather distinct, fine network. This species is named in honor of Dr. Jun Akutsu of the Department of Geology, Utsunomiya University, who offered information of the stratigraphy in the vicinity of Ogawa-machi, Nasu-gun, Tochigi Prefecture. Type locality, Geological formation and Age:– River cliff of the Naka-gawa, south of Ogawamachi, Nasu-gun, Tochigi Prefecture (Lat. 36°44'25"N., Long. 140°08'25"E.). Ogane formation. Middle Miocene. Distribution:– Ogane formation, Tochigi Prefecture; Tamatsukuri formation, Shimane Prefecture (?): Middle Miocene in age. Occurrence:– Rare in the calcareous very coarse-grained sandstone of the Ogane formation.» * — Abbreviation for Institute of Geology and Paleontology, Faculty of Science, Tohoku University, Sendai. KÔICHIRÔ MASUDA, 1962
|