Chlamys kumanodoensis Masuda, 1953
MASUDA, K. 1953. On the Miocene Pectinidae from the Environs of Sendai; Part 3. Two Miocene Pectens. Transactions and Proceedings of the Palaeontological Society of Japan [N. S.], 12: 83-87, pI. 8. [p. 85, pl. 8, figs. 9-11]
1953 Chlamys kumanodoensis Masuda, 1953
K. Masuda, 1953, plate 8.
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«Shell small, rather thick, compressed, suborbicular, equilateral except for auricles, subequivalve, although the left slightly exceeds the right in convexity; valves smooth but radiately ribbed; auricles imbricated. Right valve with numerous (about 50) faint, fine, round-topped, close-set, smooth radial threads and fine concentric growth lines; obtuse net-work present on lateral area; radial threads much wider than interspaces, rarely dichotomous and very rarely with intercalary threads; anterior auricle of right valve much larger and longer than the posterior and provided with deep byssal notch; upper half of anterior auricle with only concentric lines and its lower half with a few strong radials; posterior auricle sculptured similarly as anterior; hinge straight and with distinct cardinal crura and ctenolium; resilial pit wide and shallow. Ribs of left valve similar to those of right; anterior auricle much larger than posterior and sculptured with radial riblets, and provided with wide and shallow byssal notch; hinge with strong cardinal crura corresponding to that of right valve. Internal surface usually smooth, but sculptured with fine serration near ventral margin.
Dimensions (in mm).- Type locality and geological horizon.— Hill side about 500 m west of the Kumano Shrine, Kumanodô, Takadate-mura, Natori-gun, Miyagi Prefecture (lat. 38°11'5" N., long. 140°50'40'' E.). Moniwa formation. Early Miocene.
Depository.— Department of Geology, College of Education, Tôhoku University, Sendai, Japan. Reg. No. 1049. Remarks.— This new species of Chlamys is distinguishable from both Placopccten protomollitus (NOMURA) and P. nomurai MASUDA, n. sp., by the thicker test, larger anterior auricle, characteristic cardinal crura and also by the sculpture of the radial threads. Chlamys islandicus (MÜLLER) (ARNOLD, 1906, pp. 113-114, pl. 45, figs. 1, 1a) is also related to the present new species, but can be distinguished therefrom by the size of the shell, the square and less number of radial threads, the type of multiplication of the ribs which is by bifurcation and intercalation, the more pronounced imbrication of the left valve and by the posterior auricle being a little over one-half as long as the anterior one.» KÔICHIRÔ MASUDA, 1953
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