Mizuhopecten tokyoensis tokyoensis (Tokunaga, 1906)
TOKUNAGA, S. 1906. Fossils from the Environs of Tokyo. Journal of the College of Science, Imperial University of Tokyo, 21 (2): 1-96, pls. 1-6. [p. 65, pl. 5, figs. 1-10]
1906 Pecten tokyoensis Tokunaga, 1906
1933 Pecten (Patinopecten) taiwanus Nomura, 1933
1962 Patinopecten (Patinopecten) tokyoensis sematensis Akiyama, 1962
1933 Pecten (Patinopecten) taiwanus Nomura, 1933
1962 Patinopecten (Patinopecten) tokyoensis sematensis Akiyama, 1962
S. Tokunaga, 1906, plate 5.
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«Shell very large reaching 150 mm in length, equilateral, inequivalved, thin, nearly round in outline. Right valve strongly swollen; surface with undulating ribs and furrows; ribs very broad without any distinct limit toward the interstices; they number three or more near the central part of the shell, where each rib is broadest at the ventral margin of the shell, being about 3 mm in breadth, and again divided into three or more riblets; near the anterior and posterior portion of the shell broad ribs are separated by a very narrow interspace, and a few coarse lines of growth are visible; in the younger specimens, the furrows and ribs are more sharply bordered, the interspace being wider; ears nearly symmetrical, radially ribbed, the anterior one only slightly notched. Left valve almost flat, only very slightly swollen; ribs few, eight in number, sharp and keel-like beneath the umbones, but becoming less sharp near the ventral margin; interspaces broad and smooth, with very fine conoentric scaly lines; ears radiately striated, the anterior one higher and furnished with broad grooves.
This species which is abundant at Oji, and 1n some Tertiary districts in Japan, was identified by Brauns with Pecten plica L., but according to my own observations, there exist many points of difference between the two. P. plica L. is a small shell with a very small auricle, nearly equal blunt radial striations, and only three central ribs and two much smaller ones in each valve. These characters alone are sufficient to prove that they do not belong to the same species.»
SHIGEYASU TOKUNAGA, 1906
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«Remarks: The specimens collected from the Toukoushan Formation in the Houlung area, Miaoli Hsien, take the following description: Shell very small in size, thin, suborbicuar in outline, compressed, subequilateral, inequivalve; valves radiately ribbed, forming an angle of about 95° at the apex. Right valve slightly inflated, with four, rather low, rounded radial ribs in the central part of the disc, a few, very fine subsidiary radial threads at the submargins and prominent fine tessellations; radial ribs much broader then their interspaces, sometimes with a few, faint, fine radial threads on the surface; anterior auricle with a shallow byssal notch and with fine radial threads and fine tessellations. Left valve nearly flat, with four roof-shaped, distinct, fine radial ribs in the central part and a few fine radial threads at submargins and prominent tessellations; radial ribs much narower than their shallow interspaces; interspaces sometimes with line radial threads tending to obsolete ventrally with growth; auricles large, nearly equal to each other, with a few fine radial threads and prominent tessellations. The interior surface is strongly folded corresponding to the radial ribs on the surface.
In 1933 Nomura described Pecten (Patinopecten) taiwanus from his Byoritsu Beds, Miaoli, based upon only one water worn small right valve (height 16 mm, length 17 mm, depth ca. 3 mm), and he distinguished it from tokyoensis by its having somewhat different radial ribs. However, upon re-examination of the type specimen (IGPS, coll. cat. no. 45007) and several newly collected specimens from the so-called Byoritsu Beds at Houlung in Miaoli Hsien, it became evident that the so-called taiwanus should be included in tokyoensis because the younger shells of tokyoensis are quite similar to those of the so-called taiwanus. The so-called taiwanus can be distinguished from tokyoensis hokurikuensis Akiyama (1962) described from the Pliocene Himi Formation, Toyama Prefecture, Japan, by its low radial ribs and a few, rather distinct, fine radial threads at the submargins in the right valve, but it is difficult to distinguish it from the latter on the basis of the left valve. Also, judged from the description and ligures of Shuto (1960) the writers consider that Shuto's taiwanus from the Takanabe Formation in Miyazaki Prefecture, Japan, differs from Nomura's taiwanus and is a synonym of tokyoensis hokurikuensis as already pointed out by Masuda (1962A). All specimens of tokyoensis from the Toukoushan Formation are very small (the largest specimen being 22 mm. in height) compared to those of the Japanese specimens (the largest being about 250 mm in height). Therefore, it is evident that all specimens from the Toukoushan Formation in Taiwan represent the immature forms of the species. In 1963 Masuda established the genus Mizuhopecten based upon Pecten yessoensis Jay, a Recent species in northern Japan, and discriminated almost all species of the so-called Patinopecten from the true Patinopecten of the West Coast of North America. The former is known from the Recent seas of the Northern Pacific and from the Tertiary and Quaternary formations in Japan, Sakhalin and Kamchatka and, unlike the latter Iacks the auricular crura which are common in the Amusium, Patinopecten or Pecten groups. Recently Waller (1991) discussed the relationships between Patinopecten and Mizuhopecten based upon the shell micro-structure and concluded that the presence of auricular crura can not be used as a uniquely derived character for separating them. However, as the auricular crura with distal denticles are considered to be one of the most important characters in the classification of pectinids (Verrill, 1897; Arnold, 1906; Masuda, 1962, 1963, etc.), it is evident that the so-called Patinopecten in the Western Pacific region should be separated from Patinopecten in the Eastern Pacific region (Masuda, 1986B).» MASUDA, K. & C. HUANG. 1994. Tertiary and Quaternary Pectinidae from northern Taiwan. Journal of the Geological Society of China. 37 (4): 497-549, pls. 1-10. [p. 523, 524]
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Mizuhopecten tokyoensis (Tokunaga, 1906); K. Masuda & C. Huang, 1994, Tertiary and Quaternary Pectinidae from northern Taiwan, plate 7, figures 5-12.
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«Eight specimens are reasonably close to this species by their small number of radial ribs which are roof-shaped on the left but divided into several riblets on the right valves. Although the largest one attains about 90 mm in length, the specimens are rather smaller in size than those reported from other Pleistocene and Pliocene localities in our country.
The habitant of this fossil species was compared by Uozumi, Takagi and Suzuki (1986) with that of the living Patinopecten yessoensis (Jay), a wellknown scallop of northwestern Pacific shallow waters, from the coexistence of these two species in several fossil assemblages of Hokkaido and the Pacific side of Honshu.» O'HARA, S. & N. NEMOTO. 1988. Pectinids from the Taga Group of the Joban Coalfield. Saito Ho-on Kai Special Publication, Professor Tamio Kotaka Commemorative Volume: 481-496, pls. 1-4. [p. 492]
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Patinopecten (Mizuhopecten) tokyoensis (Tokunaga, 1906); S. O'Hara & N. Nemoto, 1988, Pectinids from the Taga Group of the Joban Coalfield, plate 2, figure 2.
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«Shell large, rather thin, suborbicular in outline, inequivalved, equilateral except for auricles, apical angle 110-120 degrees.
Right valve moderately convex, with 7 rather high, round-topped radials which are divided into 3-5 rather shallow furrows; each interspace much narrower than ribs themselves, with a interstitial riblet; auricles with fine concentric striations and several radial threads, anterior one with byssal notch; hinge straight, with conspicuous cardinal crura and large resilial pit with lateral ridges on both margins. Left valve slightly convex, with 7 round-topped, narrow radials which become to be inconspicuous towards the ventral margin; surface furnished with reticulate sculpture on the upper half of the disc and with concentric striations and numerous fine threads on the lower half; auricles furnished with fine, conspicuous, concentric striations; hinge straight, with cardinal crura and resilial pit with lateral furrows on both margins, corresponding to the right valve. Described specimens. Exposure along the River Shakujii, Ōji, Kitaku, Tokyo, Tokyo formation. Reg. no. 17010. Comparisons. The present subspecies is somewhat allied to P. kimurai kimurai and P. murayamai murayamai, but can be distinguished therefrom by the right valve with less numerous, broad but low radials divided into 3-5 riblets and by the left valve with less numerous and less elevated radials which become inconspicuous towards the ventral. Distribution. Tokyo formation from Ōji and Tabata, Tokyo and near Tsuchiura City; Miyata formation, southern part of Miura Peninsula, Kanagawa 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. 93]
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Patinopecten (Patinopecten) tokyoensis tokyoensis (Tokunaga); M. Akiyama, 1962, Studies on the phylogeny of Patinopecten in Japan, plate 2, figures 2, 3.
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