Mizuhopecten kimurai murayamai (Yokoyama, 1926)
YOKOYAMA, M. 1926. Tertiary Mollusca from the oil-fields of Akita. Journal of the Faculty of Science, Imperial University of Tokyo [Section II: Geology, Mineralogy, Geography, Seismology], 1 (9): 377-389, pls. 44, 45. [p. 387, pl. 44, figs. 18-20]
1926 Pecten murayamai Yokoyama 1926
1957 Patinopecten shibaharensis Kanno, 1957
1957 Patinopecten hayashii Kanno, 1957
1962 Patinopecten (Patinopecten) murayamai bisecta Akiyama, 1962
1957 Patinopecten shibaharensis Kanno, 1957
1957 Patinopecten hayashii Kanno, 1957
1962 Patinopecten (Patinopecten) murayamai bisecta Akiyama, 1962
M. Yokoyama, 1926, plate 44.
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«Shell thick, compressed, orbicular, slightly higher than long. Right valve with nine, strong, broad, rounded, rigid, radiating ribs separated by intervals of about equal breadth. Ears somewhat unequal; anterior ear smaller, triangular in outline with anterior border somewhat receding below, provided with a few radiating riblets; byssal notch hardly developed; posterior ear also triangular, with posterior border somewhat convex, oblique, with upper end more anterior in position, radiately ribbed like the anterior. Left valve of the same convexity as the right, radiately ribbed; ribs nine, roof-shaped, with ridges sharp; ears triangular, subequal.
Several specimens. One of the perfect right valves is 55 millim. high, 54 millim. long, and 7.5 millim. deep; while one of the perfect left is 22 millim. high, 21.5 millim. long and 3 millim. deep. The largest right valve, which is partly broken, is 86 millim. high. Fossil occurrence. ─ Beds B: Kurosawa. Beds F: Kinonezaka». MATAJIRO YOKOYAMA, 1926 |
«Remarks. MASUDA said in his paper (1955), "with regard to Patinopecten murayamai which M, YOKOYAMA (1926) first described from two remote localities in Akita Prefecture, it should be mentioned that no type locality nor holotype was designated. Here, the writer designates Figure 20 of his (1926) plate 44 as the holotype, thus the type locality is Kurosawa, Taiheimura, Minami-Akita-gun, and the stratal unit of its occurrence is, according to YOKOYAMA's paper (1926), Beds B or the Pliocene Wakimoto formation of present day nomenclature. However, that species does not seem to occur in the horizon, but possibly from a stratigraphically lower one which crops out in the same area. It is considered that there may have been a mistake in the labels which has resulted in YOKOYAMA's reference of P. murayamai to a horizon younger than the actual range of the species ".
The writer has also doubted the stratigraphic horizon of the holotype specimen of the present species. The present species from the Suenomatsuyama formation in Iwate Prefecture has following characters. Right valves have 9 round-topped radials with sharp demarcation to interspaces a little narrower than radials. Radials are furnished usually with weak radial threads and rarely with conspicuous threads especially at the submargins of some specimens like P. moniwaensis. Left valves are provided with 9 round-topped, elevated radials rarely with radial threads on their backs like P. nakosoensis. MASUDA (1960) reported that the number of radial ribs varies from 8 to 12 on P. murayarmai population from the Sugota fornution, while its population from the Suenomatsuyama formation has a constant value, 9 regarding the number of radials. Described specimens. Anaushi, Kita-Fukuoka-machi, Ninohe-gun, Iwate Prefecture. Suenomatsuyama formation. Reg, no. 17007. Comparisons. The present species is somewhat allied to P. chichibuensis, P. tiganouraensis and P. imamurai, but can be distinguished by the right and left valves with more nurnerous radials. Type locality, Kurosawa, Taihei-mura, Minami-Akita-gun, Akita Prefecture. Wakimoto formation (?). Distributions. Higashi-Innai formation of Noto Peninsula, Ishikawa Prefecture, Orito formation of Sado Isiand, Niigata Prefecture, Oisawa formation in Yamagata Prefecture, Sugota formation in Akita Prefecture, Shiomizaki formation in Aomori Prefecture, Suenomatsuyama formation in Iwate Prefecture, Futatsugoya formation in Fukushima Prefecture and Matsuida formation of the Chichibu Basin, Saitama Prefecture.» AKIYAMA, M. 1962. Studies on the phylogeny of
Patinopecten in Japan. Science Reports of the Tokyo Kyoiku Daigaku [Section C -
Geology, Mineralogy and Geography], 8 (74): 63-122, pls. 1-8. [p. 84, 85]
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Patinopecten (Patinopecten) murayamai murayamai (Yokoyama); M. Akiyama, 1962, Studies on the phylogeny of Patinopecten in Japan, plate 4, figure 1; plate 7, figure 4.
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