Kotorapecten moniwaensis (Masuda, 1958)
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. 276, pl. 41, figs. 3-6]
1955 Chlamys egregius Itoigawa, 1955
1958 Patinopecten kagamianus moniwaensis Masuda, 1958
1958 Patinopecten kagamianus nimaensis Masuda, 1958
1958 Patinopecten kagamianus moniwaensis Masuda, 1958
1958 Patinopecten kagamianus nimaensis Masuda, 1958
K. Masuda, 1958, plate 41.
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Shell large, moderately thick, compressed, orbicular, equilateral except for auricles: right Yalve nearly equal to or a little less convex than the left; both valves radiately ribbed and forming an angle of about 100º at apex.
Right valve with about 10, rather low, round-topped radial ribs, a single or a few intercalary threads between radial ribs near the submargins, and fine concentric growth lines: radial ribs much broader than their interspaces, and divided into numerous fine riblets by shallow longitudinal furrows; longitudinal riblets on the backs of radial ribs variable in strength and number, and first appear at about half of disc length and tend to become distinct towards the ventral margin; radial ribs at the lateral extremities very low and slender, and with inlerspaces variable in breadth; interspaces between the radial ribs shallow and smooth in the central part of disc; anterior auricle furnished with wide and shallow byssal notch and rather narrow byssal area; posterior auricle sculptured with several, weak radial threads and concentric lines: hinge with simple cardinal crura, and wide and shallow resilial pit provided with lateral ridges, and furnished with ill-developed ctenolium in young shell. Left valve with stout, elevated, round-topped radial ribs and concentric growth lines, and ornamented by obtuse network: radial ribs rather sharp near the beak, tend to become rounded towards the ventral margin, and divided into a few riblets by shallow longitudinal furrows on lower half of disc: interspaces much broader than radial ribs, rather deep and smooth, and with a single or a few intercalary threads in the lateral portions of disc; anterior auricle a little larger than the posterior. and sculptured with several weak radial threads and concentric lines. Interior surface of both valves gently folded and coarsely crenated at the ventral margin. Dimensions:— Shown in Table 1. Comparison and Affinity — Patinopecten kagamianus kagamianus can be distinguished from the present one by having rather thick shell, more numerous elevated radial ribs with more numerous and more distinct radial threads on the surface of auricles than that of moniwaensis. This subspecies is related with Patinopecten kimurai (YOKOYAMA) (1925) which was described from the Mliocene Kamenoo formation (HATAI and NISIYAMA, 1952) in Fukushima Prefecture, but kimurai is distinguishable from the adult specimens of the present one by having more elevated radial ribs, less distinct and less number of faint longitudinal riblets on the backs of radial ribs in the right valve, and by the roof-shaped radial ribs which remain undivided in the left valve. llowever, at times it is difticult to distinguish the young shells of the present one from kimurai, because in the young kagamianus moniwaensis the radial ribs of the right valve lack longitudinal riblets on the backs of radial ribs, and the radial ribs of the left valve show roof-like shape with no riblet on their backs. Thus the writer considers that the present one and kimurai probably had a common ancester. Remarks:— This new subspecies is characterized by its large, rather thin shell. 9 to 13. low, round-topped radial· ribs which are much broader than their interspaces and divided into numerous fine riblets by shallow longitudinal furrows, very slender and low radial ribs at the lateral portions of disc in the right valve, and by the left valve in having elevated radial ribs which are much narrower than their interspaces and divided into a few, fine riblets by shallow longitudinal furrows, and a few. fine radial threads on the surface of auricles. Type locality, Geological formation and Age:— Moniwa, Sendai City, Miyagi Prefecture. Lat.: 38º13'N., Long. 140º47'E. Moniwa formation. Early Miocene. Depository:— Holotype, DGS. Reg. No. 3506, Paratypes, DGS, Reg. No. 3507 and No. 1476. Distribution:— Moniwa formation in Miyagi Prefecture, Nanao formation in Ishikawa Prefecture. and Yanagawa and Futatsugoya formations in Fukushima Prefecture: all Early Miocene in age.» KÔICHIRÔ MASUDA, 1958
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COMPARISON WITH FOSSIL SPECIES:— The original description of Patinopecten chichibuensis by Kanno (1960) rather conforms with the diagnostic feature of the present material. The former is however, distinguished from the latter in smaller number of radial ribs on both valves and obscure riblets on radial ribs on left valve. P. chichibuensis is reasonably referred to Kotorapecten.
K. moniwaensis resembles Kotorapecten kagamianus (Yokoyama), but can be distinguished by its more prominent radial ribs (rather large value of 100C/H) and smaller number of superimposed radial riblets on primary radial rib. Masuda (1958) pointed out that K. k. nimaensis Masuda can be distinguished from the present species in smaller ratio of shellheight to width, smaller apical angle, elevated radial ribs, rather wide and deep interspaces and fine network on right valve. But number of radial ribs is really equal between the two species and other characteristics of the former agree with the varied type of the latter. K. k. nimaensis must be treated as a synonym of the present species. According to Masuda (1958 and 1962a) Kotorapecten egregius (Itoigawa) can be distinguished from the present species by its smaller shell, intercalary threads between radial ribs, very unequal auricles, rather conspicuous byssal notch, wide byssal area and conspicuous ctenolium. But these characteristics are clearly exemplified by younger specimens of the present species. Adult specimens of K. egregius shown in Itoigawa (1982, pI. 8, figs. 1a, b, 4.) are considered to be identical 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. 109]
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Kotorapecten moniwaensis (Yokoyama); Y. Sato, 1991, Paleontological study of molluscan assemblages of the Miocene Moniwa Formation, Northeast Japan and description of their Pectinidae, plate 34, figure 2.
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«Remarks. The present subspecies is characterized by the right valve with 9 round-topped radials and the left valve with 13 stout, elevated radials both furnished with longitudinal threads.
MASUDA (1958) described this as a subspecies of P. kagamianus, based on the character of radials furnished with longitudinal threads. But the writer believes that the number of radials is a more important factor than the longitudinal threads and the former should be in preference to the latter in the classification of the genus Patinopecten. It maintains this opinion that the population of P. murayamai murayamai from the Suenomatsuyama formation includes the specimens furnished with longitudinal threads on the backs of radials like moniwaensis. The writer believes that moniwaensis is closely allied to murayamai and should rank the former as a subspecies of murayamai. Comparisons. The present subspecies is much allied to P. murayamai murayamai and P. murayamai ugoensis, but can be distinguished from the latters by the right and left valves with radials furnished with conspicuous longitudinal threads. Type locality. Moniwa, Sendai City, Miyagi Prefecture. Moniwa formation. Distribution. Moniwa formation and Yanagawa member in Miyagi Prefecture, Futatsugoya formation in Fukushima Prefecture and Nanao formation in Ishikawa 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, text-figs. 1-3 [p. 87]
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Pecten (Patinopecten ?) kagamianus Yokoyama, 1929a, p. 2; pI. 1, fig. 1 (non pI. 1, fig. 2, pl. 2, figs. 1, 2).
Pecten (Vola) kagamianus Yokoyama, Nomura and Zinbo, 1936a, pI. 20, fig. 3. Patinopecten kagamianus moniwaensis Masuda, 1958d, p. 276, pI. 41, figs. 3-6. «Remarks: – Kagamianus (s. s.) can be distinguished from the present one by having rather thick shell, more numerous radial ribs, and more abundant and more distinct radial threads on the surface of auricles. This subspecies is related to Patinopecten kimurai (Yokoyama), but is distinguishable from the adult specimens of the present one by having more elevated radial ribs, less distinct and less number of longitudinal riblets on the backs of radial ribs in the right valve, and by the roof-shaped radial ribs which remain undivided in the left valve. However, at times it is difficult to distinguish the young shell of the present one from kimurai, because in the young kagamianus moniwaensis the radial ribs of the right valve lack the longitudinal riblets on the backs of radial ribs, and the radial ribs of the left valve show roof-like shape with no riblets on their backs.
Type locality, Geological formation and Age: – Floor of the small tributary of the Natori River at Moniwa, Sendai City, Miyagi Prefecture (Lat. 38°13'N., Long. 140° 47'E.). Moniwa member of Hatatate formation. Early Miocene. Distribution: – Moniwa member of Hatatate formation, Miyagi Prefecture; Nanao formation, Ishikawa Prefecture; Yanagawa and Gyônindaki formations, Fukushima Prefecture: all Early Miocene in age. Occurrence: – Common in the granule conglomerate with some pebbles to conglomeratic very coarse-grained sandstone of the Moniwa member; few in the coarse-grained sandstone of the Yanagawa formation; rare in the medium-grained sandstone of the Nanao 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, 218]
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Pecten (Patinopecten ?) kagamianus Yokoyama; M. Yokoyama, 1929, Pliocene Shells from near Nanao, Noto, plate 1, figure 1. [non Pecten kagamianus Yokoyama, 1923: Patinopecten kagamianus moniwaensis Masuda, 1958; fide Masuda 1962a, p. 217]
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