Kotorapecten kagamianus kagamianus (Yokoyama, 1923)
YOKOYAMA, M. 1923. On some fossil Mollusca from the Neogene of Izumo. Japanese Journal of Geology and Geography, 2 (1): 1-9, pls. 1, 2. [p. 8, pl. 1, figs. 1a, 1b]
1923 Pecten kagamianus Yokoyama, 1923
1930 Pecten plicicostulatus Matsumoto, 1930
1962 Patinopecten kagamianus hokkaidoensis Kanno, 1962
1930 Pecten plicicostulatus Matsumoto, 1930
1962 Patinopecten kagamianus hokkaidoensis Kanno, 1962
M. Yokoyama, 1923, plate 1.
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«Shell large, moderately thick, much compressed (the right valve a little more than the left), orbicular, subequivalve and subequilateral. Both valves radiately ribbed. The ribs on the right valve sixteen in number, broad and flatty rounded, straight, broader than the interspaces aud with a varying number of longitudinal striae on them; the interspaces shallow, usually a little narrower than the ribs and also longitudinally striated. The ribs on the left valve about equal in number to those of the right, straight, rounded, much narrower than the interspaces and furnished wiih a few longitudinal striae which are present also on the latter. Shell-margin coarsely crenate. The ears seem to be subequal, though the anterior is a little broken. Length and height 105 mm. Thickness 25 mm.
This shell shows a distant resemblance ta Pecten caurinus Gould (Arnold, Tert. a. Quatern. Pectens of California, PI. 38, fig. 1) from the American Pliocene which, however, has more (20-25) ribs, besides some other differences. Fossil occurrence.— Kagami (a single but a nice example).» MATAJIRO YOKOYAMA, 1923
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«Remarks:– Patinopecten yamasakii (Yokoyama) somewhat resembles the present one, but it has fewer, low and rather fiat radial ribs which show tri- or bifurcation and a few or several intercalary threads in interspaces in the right valve.
Type locality, Geological formation and Age: – Kagami, Kimachi-mura, Yatsuka-gun, Shimane Prefecture (Lat. 35°25'N., Long. 132°58'E.). Kimachi formation. Middle Miocene. Distribution:– Kimachi and Fujina formations, Shimane Prefecture; Moniwa member of Hatatate formation; Nanao formation, Ishikawa Prefecture; Imagane formation, Hokkaido: Middle to Early Miocene in age. Occurrence:– Abundant in the calcareous coarse-grained sandstone and common in the granule conglomerate of the Moniwa member; few in the calcareous medium-grained sandstone of the Nanao formation; common in the medium- to coarse-grained sandstone of the Imagane 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. 217]
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«COMPARISON WITH FOSSIL SPECIES:— Eleven species were referred to subgenus Kotorapecten by Masuda (1958 and 1962a), but some of them were later transferred to another genera, i.e. iwasakiensis, kintaichiensis, yamasakii and tryblium to Masudapecten, naganoensis to Mizuhopecten and nakajimai to Nipponopecten. At present, kagamianus, moniwaensis, permirus, egregius and nimaensis are regarded to belong to the genus Kotorapecten. K. kagamianus can be distinguished from moniwaensis at species level by smaller number and lower profile of radial ribs and larger number of superimposed riblets on primary ribs and lower profile. Description of hokkaidoensis in Kanno (1962) is quite identical to the characteristics of the present species and the former is considred to be the synonym of the latter. K. permirus can be distihguished from the present species by larger number of primary ribs. Change of apical angle and ratio of height to width (H/W) with growth and fundamental pattern of multiplication of radial ribs are common in kagamianus, moniwaensis and permirus. The present species has some characters of Chlamys. Namely the present species is furnished with distinct byssal notch, ctenolium, auricular denticles (Waller, 1972) and riblets on the radial rib without seals. There characters are intermediate between the subfamily Patinopectinae and Chlamydinae.
COMPARISON WITH RECENT SPECIES:— There is no close ally to the present species among the living pectinids. But Lyropecten (Nodipecten) nodosus (Linne) and L. (N.) subnodus (Sowerby) in Atlantic somewhat resemble the present species in having several riblets on the primary rib, but can be distinguished from the latter by flat shells, smaller number of radial ribs with large and hollow nodules, larger anterior auricule and intercalary riblets between the radial ribs. Mizuhopecten yessoensis (Jay) also somewhat resembles the present species, but can be distinguished from the latter by left valve which is more convex than right one, riblets on the primary ribs, ctenolium and auricular denticle in adult stage. PHYLOGENY:— Present species resembles Kotorapecten chichibuensis Kanno (1960, p. 223, pI. 34, figs. 1-4) excepting the riblets on the radial rib and much more convex left valve. So present species is not related with this species. There is no known species with phyletic relation to the present species.» SATO, Y. 1991. Paleontological study of molluscan assemblages of the Miocene Moniwa Formation, Northeast Japan and description of their Pectinidae. Report, Geological Survey of Japan, 272: 1-249, pls. 1-34. [p. 103]
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Kotorapecten kagamianus (Yokoyama); Y. Sato, 1991, Paleontological study of molluscan assemblages of the Miocene Moniwa Formation, plate 32, figures 1-8; plate 33, figures 1-7; plate 34, figures 1, 3.
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«Comparison and Affinity:– This species resembles Patinopecten iwasakiensis (NOMURA) (1935) which was described from the Miocene Tanosawa formation at Hotatezawa, Iwasaki·mura, Nishi-Tsugarugun, Aomori Prefecture, but iwasakiensis can be distinguished from the present one by the left valve which has the radial ribs gradually increasing towards the ventral margin by division and intercalation, no longitudinal riblet on the backs of radial ribs, and by the right valve which has low radial ribs carrying two or three longitudinal shallow grooves on their tops. Patinopecten yamasakii (YOKOYAMA) (1926) which was described from the Miocene Shigarami formation at Shimosoyama, Shigarami-mura, Kami-Minochi·gun, Nagano Prefecture, also resembles the present one, but it possesses a less number of low and rather flat radial ribs which show tri- or bifurcation.
Pecten (Chlamys) kagamianus miyagiensis described by NAKAMURA (1940) from the Miocene Ôtsutsumi formation at Ôtsutsumi, Taiwa-machi, Kurokawa-gun, Miyagi Prefecture in the northern border of Sendai is considered to be a synonymy of Nanaochlamys notoensis (YOKOYAMA) (HATAI and MASUDA, 1953). In "A Note on Pecten kagamianus YOKOYAMA" HATAI (1938) mentioned that whether Pecten sp. of the kagamianus type reported from the Miocene Kunnui formation developed in southwestern Hokkaido by NAGAO and SASA (1934) is identical with OTUKA's (1936) questionable kagamianus from the Miocene Sugota formation at Ukibuta, Higashi-Yuri-mura, Yuri-gun, Akita Prefecture, or with NOMURA's (1935) s-hataii from the Miocene Tanosavva formation at Hotatezawa, Iwasaki-mura, Nishi-Tsugaru-gun, Aomori Prefecture, is a question. The writer considers that OTUKA's P. aff. kagamianus may be identical with NOMURA's species. Furthermore, HATAI has discussed the relationship between kagamianus and s-hataii, and has inferred that the relation existing between them is an interesting case of adaptation or lateral localization produced as a result of migration. Remarks:– This subspecies is characterized by its large, orbicular, compressed shell with 15 to 18, stout, round-topped radial ribs bearing a number of close-set longitudinal riblets on their backs, by the hinge with rather sirnple cardinal crura, by the ctenolium in young shells, by the wide and shallow resilial pit provided with distinct lateral ridges in the right valve, and by the left valve which is ornamented by elevated radial ribs bearing several longitudinal riblets on their backs, and by the interspaces being wider than the radial ribs and the obtuse network. The right valve is usually a little less convex than the left one or sometimes subequal to it, but it seems that the right valve is sometimes a little more convex than the left as pointed by YOKOYAMA (1923). Described specimens:– Kanagase, Ôgawara-machi, Shibata-gun, Miyagi Prefecture. Calcareous sandstone of the Moniwa formation. DGS. Reg. No. 3518. Distribution:– Kimachi formation in Shimane Prefecture, Moniwa formation in Miyagi Prefecture, and Nanao formation in Ishikawa Prefecture: all Early Miocene in age.» MASUDA, K. 1958. On the Miocene Pectinidae from the Environs of Sendai; part 12, On Pecten kagamianus Yokoyama. Transactions and Proceedings of the Palaeontological Society of Japan [N. S.], 32: 271-284, pls. 40, 41. [p. 275, 276]
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Patinopecten kagamianus kagamianus (Yokoyama), 1923; K. Masuda, 1958, On the Miocene Pectinidae from the Environs of Sendai; part 12, On Pecten kagamianus Yokoyama, plate 40, figures 4, 5.
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