Chlamys nagaoi 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. 179, pl. 20, figs. 4-6]
1962 Chlamys nagaoi Masuda, 1962
1928 Pecten (Chlamys) ashiyaensis Nagao, 1928 [partim]
1928 Pecten (Chlamys) ashiyaensis Nagao, 1928 [partim]
K. Masuda, 1962, plate 20.
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«Pecten (Chlamys) ashiyaensis Nagao, 1928, p. 39, pI. 9, fig. 10. (non Pecten (Chlamys) ashiyaensis Nagao, 1928, pI. 8, figs. 2, 17, pI. 9, figs. 1, 2, 9, 20, 21).
Holotype : – IGPS, colI. cat. no. 36440.
Description: – Shell small, rather thin, higher than long, moderately inflated, subequilateral except for auricles, subequivalve ; valves radiately ribbed, apical angle about 90°. Right valve with about 30, rather elevated, round-topped, somewhat imbricated radial ribs, imbricated, fine intercalary threads and concentric growth lines; radial ribs broader than interspaces, usually divide into two, rather distinct, subequal riblets by a rather deep longitudinal furrow or very rarely into three riblets towards ventral margin; submargins with several, finely imbricated, fine radial threads; interspaces between radial ribs with a single, fine intercalary thread which appears on lower part of disc or sometimes without; auricles moderate in size; anterior larger than posterior, with rather conspicuous byssal notch and wide byssal area, having several, imbricated, fine radial threads and concentric lines; posterior one truncated behind at about right angle, similar to anterior in sculpture; Left valve with somewhat imbricated, rounded radial ribs, imbricated, fine intercalary threads and concentric growth lines; radial ribs nearly equal to interspaces in young stage but tend to become narrower than their interspaces ventrally, usually remain undivided but sometimes divide into two riblets by a shallow longitudinal furrow; submargins with several, finely imbricated, fine radial threads; intercalary threads usually a single or sometimes two or three in number, appear on upper part of disc, secondary ones appear on about middle part of disc; anterior auricle larger than posterior with several, finely imbricated, fine radial threads and concentric lines; posterior one similar to anterior in sculpture. Interior surface gently folded. Dimensions (in mm.): – Valve Right* Right Left Left
Height 40.3 21 — 26 Length 38.4 17.5 23.5 22.5 Hinge-length — 9 15.5 -- Depth 9 3 5.3 5 * — Holotype Comparison and Affinity: – Chlamys ashiyaensis (Nagao) can be distinguished from the present one by its larger shell, slightly inflated right valve with low radial ribs which are narrower than their interspaces, a few, low intercalary threads in the interspaces and by the left valve having sculpture nearly equal to that of the right valve. Chlamys sakitoensis (Nagao) is distinguishable from nagaoi by its inequivalved shell, the right valve being more convex than the left and having more or less squarish radial ribs which are narrower than their interspaces and undivided, and by the flatly inflated left valve with sculpture nearly equal to that of the right valve.
Remarks: – This species is named in honor of the late Dr. Takumi Nagao. The present species has been illustrated by Nagao (1928) as Chlamys ashiyaensis but by the re-examination of the type specimens the writer considers that some should be referred to a new species. Type locality, Geological formation and Age: – Beach, west of the Hachiman-zaki, about 300 m. north of Wakita, Wakamatsu City, Fukuoka Prefecture (Lat. 33°55'52"N., Long. 130°44'38''E.). Wakita formation. Late Oligocene. Distribution: – Known only from the type locality. Occurrence: – Common in the conglomeratic coarse-grained sandstone.» KÔICHIRÔ MASUDA, 1962
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