Mizuhopecten poculum (Yokoyama, 1926)
YOKOYAMA, M. 1926. Tertiary Mollusca from the oil-fields of Embets and Etaibets. Journal of the Faculty of Science, Imperial University of Tokyo [Section II: Geology, Mineralogy, Geography, Seismology], 1 (7): 235-248, pls. 30-32. [p. 245, pl. 32, figs. 1-3]
1926 Pecten poculum Yokoyama, 1926
1926 Pecten kurosawaensis Yokoyama 1926
1926 Pecten kurosawaensis Yokoyama 1926
M. Yokoyama, 1926, plate 32.
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«Several fragments from which the right valve can be well restored, as there is a perfect specimen apparently from the same formation in one of the localities in Honshu.
Shell large, thick, orbicular, slightly higher than long, very inequivalve, almost equilateral. Right valve strongly convex, the convexity attaining about one-third the height, ornamented with about thirty radiating ribs which are much elevated, round-topped, occasionally showing a shallow median longitudinal groove in the lower half, and separated by deep valleys either of equal or greater breadth which are very finely and delicately scaled. Beaks swollen. Anterior ear somewhat larger than posterior with a few coarse radiating rounded ribs, and a shallow byssal notch. Left valve almost flat, also with radiating ribs which are weaker than those of the right valve. Anterior ear with four coarse radiating ribs. It attains a height of more than 130 mllim. The perfect specimen shown in fig. 1 is from Kayasawa (Yamamoto-Gori, Ugo) occurring together with Nucula insignis Ad., a species which is Tertiary as well as Recent. Fossil occurrence. — Beds A, Embets.» MATAJIRO YOKOYAMA, 1926 |
«One abraded left and three fragmentary right valves were collected. This species is characterized by its convex right valve with 35 to 40 round-topped radial ribs and almost flat left valve with 35 to 40 squarish radial ribs.
It has previously been known in the Pliocene Omma-Manganji molluscan fauna of northern Japan, especially along the Japan Sea borderland (Masuda, 1962, 1980). In view of this, the present record is probably an exceptional occurrence of the species outside the Omma-Manganji molluscan province.» O'HARA, S. & N. NEMOTO. 1988. Pectinids from the Taga Group of the Joban Coalfield. Saito Ho-on Kai Special Publication, Professor Tamio Kotaka Commemorative Volume: 481-496, pls. 1-4. [p. 492]
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Patinopecten (Mizuhopecten) poculum; S. O'Hara & N. Nemoto, 1988, Pectinids from the Taga Group of the Joban Coalfield, plate 1, figure 1.
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«Remarks: – This species is distinguishable from Patinopecten yessoensis (Jay) by its greatly inflated right valve, more radial ribs which are squarish, elevated and roundly flat-topped, and much larger auricles.
The number of radial ribs of the present species varies from about 30 to a little over 40, and the most frequent number is 36. This species was first described from the Sasaoka formation at Kasuge-zawa, Yamamoto-gun, Akita Prefecture and from the Yuchi formation at Embetsu-mura, Teshiogun, Hokkaido by Yokoyama (1926c). In the same year Yokoyama (1926f) described Pecten kurosawaensis based upon a single immature right valve from the Sasaoka formation at Kurosawa, Taihei, Akita City, Akita Prefecture, but it was not distinguished from poculum at that time. Subsequently he illustrated kurosawaensis from the Onma formation at Onma, Kanazawa City, Ishikawa Prefecture. The topotype specimens of kurosawaensis from Kurosawa indicate that the so-called kurosawaensis from Kurosawa is a synonym of poculum, and the so-called kurosawaensis from Onma is not a synonym of poculum but represents a new species. Type locality, Geological formation and Age: – East cliff of the Kasuge-zawa, immediately west of the shrine at east of Kayazawa, Fujisato-mura, Yamamoto-gun, Akita Prefecture (Lat. 40°17'42''N., Long. 140°14'34''E.). Sasaoka formation. Early Pliocene.
Distribution: – Sasaoka formation, Akita Prefecture; Narusawa formation, Aomori Prefecture; Yûchi formation, Hokkaido; Sawane formation, Niigata Prefecture; Odaira formation, Iwate Prefecture; Yamada formation, Miyagi Prefecture: all Early Pliocene in age.
Occurrence: – Abundant in the granule conglomerate and very coarse-grained sandstone of the Sasaoka formation; common in the calcareous very coarse-grained sandstone of the Sawane formation; rare in the very fine-grained sandstone of the Yamada 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. 209, 210]
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Patinopecten poculum (Yokoyama); K. Masuda, 1962, Tertiary Pectinidae of Japan, plate 24, figure 1; plate 25, figure 5.
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