Nomurachlamys Kurihara & Matsubara in Kurihara 2010
KURIHARA, Y. 2010. Middle and late Miocene marine Bivalvia from the northern Kanto region, central Japan. National Museum of Nature and Science monographs, 41: 1-87, figs. 1-30. [p. 41]
«Subgenus Nomurachlamys Kurihara and Matsubara* subgen. nov.
Type species.— Pecten kaneharai Yokoyama, 1926a. Lower Upper Miocene of Honshu, Japan.
Diagnosis.— Chlamydini with small- to large-sized, bi-convex shell; both valves sculptured by 20–28, regular, flat-topped, bi- or trifurcated radial ribs separated by interspaces each having a single interstitial riblet; shagreen microsculpture may present in the grooves on ribs and interspaces; inner disc margin distinctly carinated; dorsal margins almost straight, retaining longer than half of shell length throughout shell growth; anterior auricle larger than posterior auricle, on RV with deep byssal notch and five functional ctenolium; hinge typical of Chlamys, but RV resilial and dorsal teeth prominent.
Remarks.— Nomurachlamys subgen. nov. resembles the subgenus Chlamys [Röding, 1798] (type species: “Pecten islandicus Linn.” [= Pecten islandicus Müller, 1776] by subsequent designation) in many respects. However, Nomurachlamys subgen. nov. differs from Chlamys s.s. in having regular, bi- or trifurcated radial ribs with a single interstitial riblet in both valves, radially carinated disc margin, and the prominent resilial and dorsal hinge teeth. The new subgenus has a superficial resemblance to the genus Mimachlamys Iredale, 1929 (type species: Pecten asperrimus Lamarck, 1819 by original designation; tribe Mimachlamydini), as it shares with that genus the regular radial ribs and a deep byssal notch. Masuda (1962) referred some constituents of Nomurachlamys subgen. nov. to Mimachlamys. However, the new subgenus differs from Mimachlamys in having flat-topped primary radial ribs and the shagreen microsculpture, instead of rounded primary radial ribs and “herringbone” and “feather” type microsculpture. The shagreen microsculpture is one of the diagnostic characters of the tribe Chlamydini (Waller, 1993; Beu and Darragh, 2001). The new subgenus is also similar to the Miocene–Pliocene genus Phialopecten Marwick, 1928 (type species: Pecten triphooki Zittel, 1864, by original designation; tribe Palliolini, see Beu, 1995) in New Zealand. However, Phialopecten is distinguished from Nomurapecten subgen. nov. by having a shallower byssal notch and a larger, posteriorly oblique posterior auricle, and in lacking the shagreen microsculpture.
Nomurachlamys subgen. nov. includes the following species in addition to the type species: Chlamys (Chlamys) ishidae Masuda, 1962 from the uppermost Lower Miocene of Honshu; Pecten (Chlamys) meisensis Makiyama, 1926 from the lower Middle to upper Middle Miocene of Honshu and Korean Peninsula. Besides, Pecten miurensis Yokoyama, 1920 from the upper Upper Miocene to Lower Pliocene of Honshu, Pecten akitanus Yokoyama, 1926 from the lower Middle Miocene of Honshu, and Pecten nisataiensis Otuka, 1934 from the uppermost Lower Miocene of Honshu may be members of the new subgenus, but their subgeneric assignment are suspended herein because its external microsculpture and precise interior characters are not fully understood. Etymology.— The new subgenus is named in honor of the late Dr. Sitihei Nomura (1892–1946), who greatly contributed to our knowledge of the systematics of Neogene and Recent molluscs in Japan, combined with the pectinid genus name Chlamys. The gender is feminine.»
* Takashi Matsubara (Museum of Nature and Human Activities, Hyogo)
YUKITO KURIHARA & TAKASHI MATSUBARA, 2010
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Chlamys (Nomurachlamys) kaneharai (Yokoyama); Y. Kurihara, 2010, Middle and late Miocene marine Bivalvia from the northern Kanto region, central Japan, figures 17A-17E.
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