Pecten byoritsuensis (Nomura, 1933)
NOMURA, S. 1933. Catalogue of the Tertiary and Quaternary Mollusca from the Island of Taiwan (Formosa) in the Institute of Geology and Paleontology, Tohoku University, Sendai Japan. Part 1, Pelecypoda. Science Reports of the Tohoku University [2nd. Series -Geology], 16 (1); 1-108, pls. 1-4. [p. 57, pl. 1, figs. 4a, 4b, 5a, 5b]
1933 Pecten (Vola) byoritsuensis Nomura, 1933
S. Nomura, 1933, plate 1.
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«Shell resembling P. excavatus ANTON in general aspects; medium in size, subcircular, longer than high, strongly inequivalve, almost equilateral; sides of the disc almost straight and sloping, with the ventral margin evenly arcuated.
Right valve strongly convex with 14 or 15 radiating ribs separated by narrower interspaces; ribs subequal, squarish in cross-section, divided into three or four unequal parts by shallow grooves on top. Beak swollen, prominent, almost smooth. Left valve considerably concave and the ribs much narrower than interspaces which are often provided with an interstitial thread. Surface of both valves finely concentrically striated leaving a small umbonal area almost smooth. Ears subequal, anterior ear of the right valve furnished with a shallow notch below. Length, 40 mm.: height, 36 mm.: depth, 12 mm. (right valve). Several well preserved specimens were examined. This species is distinguished from P. sinensis SOWERBY (not P. sinensis of YOKOYAMA) by the beak of the right valve being less swollen; from P. sulcicostatus SOWERBY by less number of ribs. Fossil occurrence: Byôritsu Beds.— Wangwa: station 8; Reg. No. 44796. Wangwa: station 40; Reg. No. 44798. Chû-tsûshô-wan: station 47; Reg. No. 44797. The upper course of Sairyôkyô; Reg. No. 45001.» SHICHIHEI NOMURA, 1933
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«Pecten (Vola) byoritsuensis Nomura, 1933, p.57, pl.1, figs. 4a-b, 5a-b.
Pecten (Pecten) byoritsuensis. Amano and Ohno, 1988, p. 40, pI. 1, figs. 1-6, 9-12; pI. 2, figs. 1, 3, 5-10. Holotype: IGPS* coll. cat. no. 45001 (*Abbreviation for Institute of Geology and Palaeontology, Tohoku University, Sendai, Japan).
Remarks: Nomura's original description is as follows: "Shell resembling P. excavatus Anton in general aspect; medium in size, subcircular, longer than high, strongly inequivalve, almost equilateral; sides of the disc almost straight and sloping, with the ventral margin evenly arcuated. Right valve strongly convex with 14 to 15 radiating ribs separated by narrower interspaces; ribs subequal, squarish in cross-section, divided into three or four unequal parts by shallow grooves on top; beak swollen, prominent, almost smooth. Left valve considerably concave and the ribs much narrower than interspaces which are often provided with an interstitial thread. Surface of both valves finely concentrically striated leaving a small umbonal area almost smooth. Ears subequal, anterior ear of the right valve furnished with a shallow notch below. Length, 40 mm: Hieght 36 mm: Depth 12 mm (right valve)". The specimens collected from the Toukoushan Formation in the Houlung area, Miaoli Hsien, take the following description: Shell rather small in size, rather thick, suborbicular in outline, subequilateral, strongly inequivalve; valves radiately ribbed, forming an angle of about 100° at the apex. Right valve greatly inflated, with about 18, rather low, rounded radial ribs in which one or two radial ribs are at submargins and very low, fine rather distinct lamellated concentric lines; the upper part of the disc nearly smooth, but radial ribs tend to become distinct and are divided into several, fine, irregular radial threads by shallow longitudinal furrows with rather distinct, somewhat lamellated concentric lines with growth; interspaces between radial ribs narrower than the ribs themselves, with nearly equally spaced lamellated, fine concentric lines and sometimes with low, faint, fine intercalary threads; auricles nearly equal to each other, and with fine radial threads and concentric lines. Left valve considerably concave, with more or less squarish, low radial ribs, intercalary threads and nearly equally spaced lamellated fine concentric lines; the upper part of the disc nearly smooth, a little inflated and tends to became concave with growth. Hinge with distinct cardinal crura, and with fine provinculum. Interior surface with distinct paired squarish internal ribs. Pecten sinensis Sowerby, a Recent species in Southwestern Pacific, resembles the present species in having radial threads on the surface of the radial ribs, but it is distinguishable from the present one by its more greatly inflated large right valve with a smaller number of flat-topped radial ribs and deeply concaved left valve. Sometimes the present species has very low radial ribs tending to be divided into two parts by a very shallow longitudinal furrow and to become obsolete towards the ventral margin in the right valve. Dimensions (in mm.):
Type locality: Sairyokyo (Yseiliao Bridge in current name), Tainan Hsien (Byoritsu Beds).
Geologic distribution: Byoritsu Beds in Tainan Hsien and Toukoushan Formation in Miaoli Hsien, Taiwan; Omma Formation in Ishikawa Prefecture, Japan. Geologic range: Pleistocene. 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. 519, 520]
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Pecten (s.s.) byoritsuensis Nomura, 1933; K. Masuda and C. Huang, 1994, Tertiary and Quaternary Pectinidae from northern Taiwan, plate 5, figures 19-23; plate 6, figures 1-6.
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