Kotorapecten permirus (Yokoyama, 1926)
YOKOYAMA, M. 1926. On some Pliocene shells from Kaga and Noto. Journal of the Geological Society of Tokyo, 33 (391): 9-11, pl. 1. [p. 10, pl. 1, fig. 1]
1926 Pecten permirus Yokoyama, 1926
1926 Pecten permirus var. paucicosta Yokoyama, 1926
1926 Pecten permirus var. paucicosta Yokoyama, 1926
«Shell Iarge, moderately thick, orbicular in outline, rather compressed, equilateral, inequivalve. Left valve: Somewhat convex, radiatly ribbed; ribs about twenty or a Iittle more in number, narrower than interspaces, round-topped, longitudinally costellate (wiith costellae four or more in number and broader than interspaces), regular, subequidistant except at the extreme lateral portions of the shell where many unequal, close or more or Iess distant riblets appear instead; interspeces between the regular ribs usually smooth in the younger specimes except near the lateral margins of the shell where an intercalary riblet may be present; in full grown ones, however, all the interspaces may be more or less longitudinally striate; ears triangular, somewhat unequal (anterior Iarger) radiately ribbed (ribs ten to twelve in number) with a lateral borders somewhat oblique and curved. Right valve: Almost flat, radiately ribbed like the left valve, with ribs equal in number to those of the latter and also longitudinally costellate on top, though flatter and broader, the breadth being generally equal to that of the interspaces; ears radiately ribbed, markedly unequal, the anterior being larger, strongly curved at anterior border and provided with a distinct byssal notch below; the posterior ear is Iike that of the left valve.
This shell attains a large size. The fragments present show that the largest specimen is at least one and a half times the largest perfect one we possess. The latter (fig. 1) is a left valve, 110 millim. high, 118 millim. Iong and 18 millim. deep. The right valves are all in fragments. The left valve shown in fig. 2 has only fifteeen regular ribs. It is probably an abnormal form; but as we possess at present no intermediate ones connecting it with the typical, I provisionally separate it as var. paucicostata. It is 80 millim. high, 82 millim. Iong and 13 millim. deep. The age of the Noto shells too is very probaly Upper Pliocene Iike those of Kaga.» MATAJIRO YOKOYAMA, 1926
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«Remarks: – This subspecies can be distinguished from kagamianus (s. s.) by the thick shell, larger number of radial ribs, characteristics of radial ribs and auricles, and the hinge area.
This subspecies was described by Yokoyama (1926b) from the Nanao formation as Pecten permirus and Pecten permirus var. paucicostata. Later, the same author (1929a) included them into the synonym of kagamianus with statement that it shows considerable variation in the number and size of radial ribs. Type locality, Geological formation and Age: – Road-side cliff at Iwaya, about 750 m. west of Nanao station, Nanao City, Ishikawa Prefecture (Lat. 37°01'03"N., Long. 136°57'04"E.). Nanao formation. Early Miocene. Distribution: – Nanao formation, Ishikawa Prefecture; Gido formation, Miyagi Prefecture; Shiratori member of Kadonosawa formation, Iwate Prefecture: all Early Miocene in age. Occurrence: – Abundant in the calcareous medium-grained sandstone and common in the medium-grained sandstone of the Nanao formation; abundant in the conglomeratic very coarse-grained sandstone and common in the medium-grained sandstone of the Oido formation.» MASUDA, K. 1962. Tertiary Pectinidae of Japan. Science Reports of the Tohoku University [2nd. Series -Geology], 33 (2): 117-238, pls. 18-27. [p. 218]
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«Shell large, thick, compressed, orbicular, equilateral except for auricles; right valve a little less convex or subequal to the left; both valves radiately ribbed and forming an angle of about 100° at apex.
Right valve with 21 to 29, stout, elevated, round-topped radial ribs and fine concentric growth lines: radial ribs broader than their interspaces, and divided into several, fine riblets by shallow longitudinal furrows; riblets on the backs of radial ribs usually appear on upper half of disc. and tend to become distinct towards the ventral margin; radial ribs at the lateral extremities very weak and slender: interspaces between the radial ribs deep and smooth, but shallow near the submargins and sometimes with a single or rarely a few, very weak intercalary threads; anterior auricle sculptured with several, fine radial threads and concentric Iines, and furnished with rather wide and shallow byssal notch and rather wide byssal area: posterior one similar to anterior in sculpture; hinge with conspicuous cardinal crura, rarely with rather flat hinge plate with very faint striae parallel to the hinge line in full adult specimen, deep and wide resilial pit provided with distinct lateral ridges, and ill-developed ctenolium in young shell. Left valve with elevated, slender radial ribs and concentric growth lines, and ornamented by obtuse network; radial ribs much narrower than their interspaces, divided into a few, tine riblets by shallow longitudinal furrows on lower half of disc; radial ribs at lateral extremities very weak and slender. and with a single or a few, fine intercalary threads in their interspaces; auricles sculptured with about ten radial threads and concentric lines, and anterior one somewhat larger than the posterior. Interior surface of both valves gently folded and coarsely crenated at the ventral margin. Dimensions: — Shown in Table 1. Comparison and Affinity: — This subspecies can be distinguished from kagamianus kagamianus, kagamianus moniwaensis and kagamianus nimaensis by the thick shell, larger number of radial ribs, characteristics of radial ribs and auricles, and the hinge area. Remarks: — This subspecies is characterized by its rather thick, compressed shell, 21 to 29, elevated, round-topped radial ribs which are divided into several, fine riblets, conspicuous cardinal crura, deep and wide resilial pit provided with distinct lateral ridges, and rather wide byssal area. Type locality, Geological formation and Age: — Iwaya, Nanao City, Ishikawa Prefecture. Lat. 37°111'03'' N., Long. 136°57'04''E. Nanao formation. Early Miocene. Depository:— Lectotype, University of Tokyo (YOKOYAMA, 1926, pl. 2, fig. 1, here designated). Described specimens: — lwaya, Nanao City, Ishikawa Prefecture. Calcareous sandstone of Nanao formation. DGS, Reg. No. 1888. Distribution: — Nanao formation in Ishikawa Prefecture and Oido formation in Miyagi Prefecture: both Early Miocene in age.» MASUDA, K. 1958. On the Miocene Pectinidae from the Environs of Sendai; part 12, On Pecten kagamianus Yokoyama. Transactions and Proceedings of the Palaeontological Society of Japan [N. S.], 32: 271-284. [p. 279]
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Patinopecten kagamianus permirus (Yokoyama), 1926; K. Masuda, 1958, On the Miocene Pectinidae from the Environs of Sendai; part 12, On Pecten kagamianus Yokoyama, plate 40, figures 1a, 1b, 2, 3.
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