Nomurachlamys kaneharai (Yokoyama, 1926)
YOKOYAMA, M. 1926. Tertiary Mollusca from Shiobara and Shimotsuke. Journal of the Faculty of Science, Imperial University of Tokyo [Section II: Geology, Mineralogy, Geography, Seismology], 1 (4): 127-138, pls. 16-20. [p. 135, pl. 18, fig 1; pl. 19, figs. 1-2, 5-7]
1926 Pecten kaneharai Yokoyama, 1926
M. Yokoyama, 1926, plates 18, 19.
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«Shell large, compressed, orbicular, somewhat inequivalve. Right valve slightly more convex than left, ornamented by more than 20 radiating ribs separated by valleys usually a little broader than the ribs themselves; ribs high and elevated, rounded, divided into three parts by two longitudinal furrows with the middle part broader than the lateral ones and more elevated; valleys also with a singte intercalary riblet; ribs as well as riblets closely scaled; ears unequal, anterior f'longated, and provided with a few scaled radiating riblets and a deep byssal notch below, posterior triangular with lateral (posterior) side shortest. Left valve slightly flatter than right, with surface-sculpture similar, but with the ribs usually bipartite instead of tripartite and the intercalaries more prominent with occasionally a smaller intercalary between them and the main ribs; ears both triangular.
The largest specimen attains a diameter of 100 millim. It is much to be regretted that, in spite of its very frequent occurrence it is almost impossible to secure perfect specimens. Moreover, they are so firmly attached to the stone that what we get are either their casts or those with only their inner side exposed. On this account, it is difficult even to distinguish the right valve from the left. Fossil occurrence.— Zones II and III (most frequent).» MATAJIRO YOKOYAMA, 1926
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«Discussion.— The specimens from the Ichibu Formation have a large-sized, ovate shell with ca. 21 regularly spaced, rather high, flat-topped radial ribs which tend to become weakly bifurcated with shell growth, an interstitial rib, a large anterior auricle with deep byssal notch and strong byssal fasciole in the right valve, and weakly crenulated ventral margin. They closely resembles Chlamys (Nomurachlamys) kaneharai (Yokoyama, 1926a), although the latter species generally has rooftopped, narrower, trifurcated radial ribs with strong scaly sculpture (e.g. Yokoyama, 1931; Masuda, 1956a). However, Ch. (N.) kaneharai may have bifurcated, flattopped radial ribs lacking any distinct scaly sculpture, as shown by Kurihara (2010). In addition, the younger shell characters of Ch. (N.) kaneharai from the Upper Miocene Kubota Formation in Fukushima Prefecture, Northeast Japan, are quite identical with the Ichibu specimens (Iwasaki, 1970a). Therefore, the specimens from the Ichibu Formation are considered to fall within the intraspecific variation of Ch. (N.) kaneharai.
Chlamys (Nomurachlamys) kaneharai closely resembles Chlamys (Nomurachlamys) meisensis (Makiyama, 1936) from the middle Miocene Mankodô Formation in the Meisen [=Meongcheon] area, North Korea. However, Ch. (N.) kaneharai is distinguished from Ch. (N.) meisensis by having a larger anterior auricle with a deeper byssal notch and a stronger byssal fasciole in the right valve. As pointed out by Kurihara (2010), Chlamys hataii Masuda and Akutsu, 1956 from the middle Miocene Nagaoka Formation in Tochigi Prefecture is a junior synonym of Ch. (N.) meisensis. Chlamys oidensis Hatai, Masuda and Noda, 1974, from the middle Miocene Oido Formation in Miyagi Prefecture, Northeast Japan, was formerly considered to be closely related to Ch. (N.) kaneharai (e.g. Hatai et al., 1974). However, its holotype (IGPS 64419; articulated valve) is considered to fall within the intraspecific variation of Chlamys (Leochlamys) arakawai (Nomura, 1935), as shown by Sato (1991). On the other hand, its paratype (IGPS 94427; left valve) is referred to Chlamys (Leochlamys) ingeniosa (Yokoyama, 1929) on the basis of the shell outline and external shell sculpture. The left valves of presumable topotypes of Ch. (L.) ingeniosa were first described and illustrated by Nomura and Tazaki (2007). Pecten miurensis Yokoyama, 1920 from the uppermost Miocene–lower Pliocene Zushi Formation in the Miura Peninsula, central Japan, is another allied species, but is distinguished from Ch. (N.) kaneharai in having rounded and a greater number of (ca 26) radial ribs without bifurcation or trifurcation. As the former species does not have any shagreen microsculpture, it is probably referable to the genus Mimachlamys Iredale, 1929 (type species: Pecten asperrimus Lamarck, 1819, by original designation). Distribution.— Latest middle–late Miocene: Aosawa and Hongô formations in Yamagata Prefecture (Ogasawara et al., 1985, as Chlamys aff. kotorana Otuka; Oba et al., 2005); Ôtsutsumi, Nanakita, Tsunaki, Kanagase and Yamairi formations in Miyagi Prefecture (Nomura and Hatai, 1937; Masuda, 1956a; Oishi et al., 1992; Sato et al., 2002; Saijo et al., 2009b); Kubota Formation in Fukushima Prefecture (Yokoyama, 1931; Iwasaki, 1970a, b; Nemoto and O’Hara, 2003); Kanomatazawa, Iriéno and Yamamoto formations in Tochigi Prefecture (Yokoyama, 1926a; Furusawa et al., 1987; Nunokawa et al., 2004); Itahana Formation in Gunma Prefecture (Kurihara, 2010); Nakatsukyô Formation in Yamanashi and Kanagawa prefectures (Shibata, 1956); Aoki Formation in Nagano Prefecture (Narita et al., 2001); Matsué and Ichibu formations in Shimane Prefecture (Nomura and Hatai, 1939; Takayasu, 1980, as Ch. cf. kaneharai; this study).» MATSUBARA, T., I. NORO, Y. MATSUURA & T. IRIZUKI. 2014. Miocene Mollusca from the Ichibu Formation on Nishinoshima Island, Oki Islands, Southwest Japan. Paleontological Research, 18 (1): 6-32, figs. 1-11. [p. 18, 19]
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Chlamys (Nomurachlamys) kaneharai (Yokoyama); T. Matsubara, I. Noro, Y. Matsuura & T. Irizuki, 2014, Miocene Mollusca from the Ichibu Formation on Nishinoshima Island, Oki Islands, Southwest Japan, figures 7.2, 7.3, 7.6, 7.9.
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«Nom. Jap., Kanehara-itayagai n. n.
Pecten kaneharai YOKOYAMA, Jour. Fac. Sci. Imp. Univ. Tokyo, Sec. 2, Vol. 1, Pt. 4, p. 135, pl. 18, fig. 1; pl. 19, figs. 1, 2, 5-7, 1926.
Pecten kaneharai YOKOYAMA. NOMURA and HATAI, SaitO Ho-on Kai Mus., Res. Bull., No. 10, p. 119, pl. 13, figs. 3, 4, 1936. Localities: Matumori (abundant), Reg. No. 2632. Kokuda (frequent), Reg. No. 10860. Isikura (abundant), Reg. No. 10878. Kumagaya (frequent), Reg. No. 10864. Northeast of Dôbayama (abundant), Reg. No. 10855.
NOMURA, S. & K. HATAI. 1937. A List of the Miocene Mollusca and Brachiopoda Collected from the Region Lying North of the Nanakita River in the Vicinity of Sendai, Rikuzen Province, Japan. Saito Ho-on Kai Museum of Natural History Research Bulletin, 13: 121-145, pls. 17-21. [p. 127, pl. 18, figs. 1, 2]
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Pecten (Chlamys) kaneharai Yokoyama; S. Nomura & K. Hatai, 1937, A List of the Miocene Mollusca and Brachiopoda Collected from the Region Lying North of the Nanakita River in the Vicinity of Sendai, Rikuzen Province, Japan, plate 18, figures 1, 2.
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