Mizuhopecten planicostulatus (Nomura & Niino, 1932)
NOMURA, S. & H. NIINO. 1932. Fossil Mollusca from Izu and Hakone. Science Reports of the Tohoku University [2nd. Series - Geology], 15 (3): 169-192 [p. 177, pl. 11, figs. 2-5]
1932 Pecten (Patinopecten) planicostulatus Nomura & Niino, 1932
S. Nomura & H. Niino, 1932,
plate 11. |
«Shell large, about 110 mm. in height, compressed, length nearly equal to height, subequivalve, subequilateral; sides straight, with margins smooth; umbonal angle about 110º. Test rather thin. Right valve ornamented by 18 low, rounded, subequal ribs which are sometimes dichotomous or branching; in some specimens the ribs are almost obsolete near the ventral margin; interspaces subequal, very shallow, much narrower than the ribs, rarely provided with interstitial riblets; whole surface covered by numerous fine growth lines and a few stronger periodic ones; hinge line less than one-half of disk-length. Ears subequal in length; anterior ear rounded in front and ornamented by almost obsolete radials as well as concentric lines of growth; byssal notch rather shallow and broad; posterior ear is obliquely truncated, ornamented by only concentric lines. Left valve quite similar to the right except for almost equal ears.
Occurrence: Ichiyama near Yugashima (Shirahama Group).»
SHICHIHEI NOMURA & HIROSHI NIINO, 1932
|
«More than two hundred specimens of various size were collected. Based on biometric analysis of morphological variations in shell-form and surface ornamentation,
they were identified by the present writers (O'Hara and Nemoto, 1975) as Patinopecten pseudoyessoensis which was first described by Akiyama and Miyajima (1960) from the upper Pliocene Nojima Formation of Miura Peninsula. Since then, due to their considerable range of variation of shape and number of radial ribs, the writers have been engaged in studying the critical discrimination of this species from allied forms from the Pliocene of Japan and adjacent areas. As a result of this study, the writers are now inclined to believe that the degree of variation in outline of these Futatsu-numa specimens appears to grade into that of Pecten planicostulatus decribed by Nomura and Niino (1932) from the Pliocene Shirahama Formation of Izu Peninsula. A full description has already been given (O'Hara and Nemoto, 1975). This species is known to occur commonly in the upper Pliocene Kurotaki Formation of Boso Peninsula (Masuda, L962, 1980; O'Hara and Takahashi, 1975).» 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. 491]
|
Patinopecten (Mizuhopecten) planicostulatus; S. O'Hara & N. Nemoto, 1988, Pectinids from the Taga Group of the Joban Coalfield, pl. 4, figs. 1, 2.
|
«Cotype: – IGPS, colI. cat. no. 48584.
Remarks: – This species can be distinguished from Patinopecten yessoensis (Jay) by its slightly inflated right valve having lower radial ribs which tend to become obsolete towards ventral margin and divide into two or three riblets by shallow longitudinal furrows. This species was described based upon deformed specimens. It is noticed that the specimens from the Pliocene Kurotaki formation are rather large in size compared with those from the Shirahama formation. Type locality, Geological formation and Age: – Bank of the pond, about 250 m. east of the shrine at Ichiyama, Kami-Kamo-mura, Tagata-gun, Shizuoka Prefecture (Lat. 34°44'N., Long. 138°56'E.). Shirahama formation. Early Pliocene. Distribution: – Shirahama formation, Shizuoka Prefecture; Kurotaki formation, Chiba Prefecture: both Early Pliocene in age. Occurrence: – Common in the calcareous medium-grained sandstone of the Shirahama formation.» MASUDA, K. 1962. Tertiary Pectinidae of Japan. The Science Reports of the Tōhoku University [2nd. Series -Geology], 33 (2): 117-238, pls. 18-27. [p. 209]
|
Patinopecten planicostulatus (Nomura and Niino); K. Masuda, 1962, Tertiary Pectinidae of Japan, plate 23, figure 11; plate. 27, figure 9.
|