Amussiopecten kankoensis (Tan, 1971)
TAN, K. 1971. The Paleogene stratigraphy and paleontology of Taiwan. Publishing Committee of the Manuscript by the late Professor Dr. Keinosuke Tan, Akita, Japan, pp. 1-55, 16 pls. [p. 34, pl. 1, figs. 1-6]
1971 Pecten (Amusiopecten) [sic] kankoensis Tan, 1971
Amussiopecten kankoensis (Tan, 1971); Masuda, K. & C. Huang, 1990, Miocene Pelecypoda in the western foorhills of northern Taiwan, plate 4, figures 12-14.
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«Shell small to medium sized, slightly inflated, orbicular in outline, nearly as long as high, equilateral except for ears, inequivalve, radiately ribbed on the external surface as well as on the internal.
Right valve: Shell slightly convex, more convex than left: about 19 ribs, flat-topped, rectangular in crosssection, becoming round towards umbonal region, decreasing in height towards ventral margin, interstices with flat-bottoms, a little narrower or as broad as ribs themselves; ribs and interstices marked by obsolate concentric striae. Hinge line straight, rather long, equal to nearly one-half of shell length. Both ears moderately large, nearly equal in form and size: anterior ear with faint radial lines, posterior ear with many longitudinal striations; byssal notch weak. Internal surface sculpture corresponding to external surface in general, the number of ribs of internal surface are two or three less than on external surface, owing to minor riblets at anterior and posterior ends of disc not being represented on inner side. Ligamental pit triangular in shape, measuring 2.5mm in base line, 40 mm in height. Left valve: Anterior and posterior ears more similar to each other than in the case of right valve, as the byssal notch in the anterior ear is wanting. Radiating ribs narrower and rounder than those of right valve, consequently interstices considerably broader than ribs themselves. Ribs becoming lower and flatter toward ventral margin, but higher and rounder toward umbonal region. Interstices between radial ribs in right and left valves depressed in middle so that both margins of interstices remain higher, assuming narrow, sharp ridges. Internal ribs in the present specimens evidently indicated by narrow grooves in internal moulds. Internal ribs (or sharp-ridge) are weaker than in the most species of Amusiopecten [sic] or Amusium. Internal ribs are restricted to lower third of shell length.» KEINOSUKE TAN, 1971
[Original description from Kôichirô Masuda & Chi-Yue Huang, 1990] |
«Pecten (Amusiopecten) kankoensis Tan, 1971, p. 34, pI. 1, figs. 1-6.
Amussiopecten kankoensis. Kanno and Chang, 1973, p. 200, pI. 30, figs. 1-10, pI. 31, figs. 1-3; Kanno and Chung, 1973, p. 111, pI. 10, figs. 10-13; Masuda and Huang, 1990. p. 148, pI. 4, figs. 12-14. Syntype: NTUM 93-223
Remarks: The original description is quoted below: "The shell small to medium sized, slightly inflated, orbicular in outline, nearly as long as high, equilateral except for ears, inequivalve, radiately ribbed on the external surface as well as on the internal. Right valve: Shell slightly convex, more convex than left: about 19 ribs, flat-topped, rectangular in cross-section, becoming round towards umbonal region, decreasing in height towards ventral margin, interstices with flat-bottoms, a little narrower or as broad as ribs themselves; ribs and interstices marked by obsolete concentric striae. Hinge-line straight, rather long, equal to nearly one-half of shell length. Both ears moderately large, nearly equal in form and size; anterior car with faint radial lines, posterior ear with many longitudinal striations; byssal notch weak. Internal surface sculpture corresponding to external surface in general, the number of ribs of internal surface are two or three less than on external surface, owing to minor riblets at anterior and posterior ends of disc not being represented on inner side. Ligamental pit triangular in shape, measuring 2.5 mm in base line, 40 mm in height. Left valve: Anterior and posterior ears more similar to each other than in the case of right valve, as the byssal notch in the anterior ear is wanting. Radiating ribs narrower and rounder than those of right valve; consequently interstices considerably broader than ribs themselves. Ribs becoming lower and flatter toward ventral margin, but higher and rounder toward umbonal region. Interstices between radial ribs in right and left valves depressed in middle so that both margins of interstices remain higher, assuming narrow, sharp ridges. Internal ribs (or sharp ridge) is weaker in the most species of Amusiopecten [sic] or Amusium. Internal ribs are restricted to lower third of shell length." The specimens collected from the Shihszeku Formation in Nantou Hsien, take the following description: Shell medium in size and thickness, compressed, orbicular in outline, equilateral; right valve more convex than the left one; radiately ribbed and forming an angle of about 100° at the apex. Right valve gently inflated, with about 20 prominent, roundly flat-topped radial ribs and fine incremental lines; radial ribs broader than their nearly flatbottomed interspaces, usually tending to become lower and obsolete towards the ventral margin; auricles more or less angulated, with fine radial threads and concentric lines; anterior auricle with a shallow and wide byssal notch. Left valve nearly flat except for a little inflated upper part of the disc, with distinct, rounded, low radial ribs and fine, somewhat lamellated, rather distinct incremental lines; auricles straight. Interior surface with distinct paired internal ribs extending from the middle part of the disc to ventral margin. Hinge with rather simple cardinal crura having auricular crura. Amussiopecten yabei (Nomura, 1933), a common species of the Miocene formations in Taiwan and southern Japan, can be distinguished from the present one by its rather large shell and smaller number of flatly round-topped, low ridial ribs and distinct internal ribs extending from the upper part of the disc to the ventral margin. Dimensions (in mm.):
Type locality: Sokutu (fsuku) Formation in Kankou village, Shihting-Hsiang, Taipei Hsien.
Geologic distribution: Wuchihshan, Aoti and Mushan Formations and Urai Group in Taipei Hsien; Shuichangliu and Shihszeku Formations in Nantou Hsien, Taiwan. Geologic range: Late Oligocene.» MASUDA, K. & C. HUANG. 1990. Tertiary and Quaternary Pectinidae from northern Taiwan. Journal of the Geological Society of China, 37 (4): 497-549, pls. 1-10. [p. 526, 527]
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Amussiopecten kankoensis (Tan, 1971); K. Masuda and C. Huang, 1993,Tertiary and Quaternary Pectinidae from northern Taiwan, plate 8, figures 4-7; plate 9, figures 1-5.
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