Mimachlamys satoi (Yokoyama, 1928)
YOKOYAMA, M. 1928. Mollusca from the Oil-Field of the Island of Taiwan. Imperial Geological Survey of Japan, Report, 101: 1-112, pls. 1-18. [p. 94, pl. 13, figs. 13-14; pl. 14, fig. 2]
1928 Pecten (Chlamys) satoi Yokoyama, 1928
1932 Pecten kakisakiensis Nomura & Niino, 1932
1960 Gloripallium satowi Shuto 1960
1932 Pecten kakisakiensis Nomura & Niino, 1932
1960 Gloripallium satowi Shuto 1960
M. Yokoyama, 1928, plates 13, 14.
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«Shell moderate in size in,orbicular, slightly higher than long, somewhat inequivalve. Left valve flatly convex, ornamented with about thirty radiating ribs, each accompanied by a minor one on both sides and close to it; interspaces between ribs somewhat narrower than the ribs themselves, and both covered with fine scales. Ears unequal; posterior much larger than
anterior. Right valve flatter than left and almost flat with sculpture similar to the latter; ears less unequal with posterior triangular in shape. Proportions of height to length and depth are on an average as follows: In the left valve 10 : 9 : 2, in the right valve 10 : 9 : 1.1. The largest example we have is a left valve measuring 52 millim in height. In sculpture this species resembles Pecten australis Sow. (Reeve, Conch. Icon., pl. 25, fig. 103) living in Australia. But the ribs are less, and the valves more equal in the latter. Fossil occurrence.— Upper Byoritz Beds: (1) Hōtosak, Rinkō Shō Taihok (蚕北州新m:郡林口!主賓斗底); (2) Ubikō Tsūshō Shō (iiII符庄鳥居坑) and (3) Tanbunko (淡文湖) in Shinchik (新竹州首栗郡), Lower Byoriz Beds: West of Bitō Zuihō Shō, Taihok (豪北州基隆郡瑞芳庄鼻頭). Upper Byoriz Beds: Banahō Shinchik (新竹州大湖郡馬那邦).» MATAJIRO YOKOYAMA, 1928
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«Description: Shell large in size, medium in thickness, higher than long, equilateral except for auricles, inequivalve; left valve more inflated tha¡r right one; valves radiately ribbed, forming an angle of a little less than 90° at the apex. Right valve slightly inflated, with 25 to 30 conspicuous, more or less squarish, imbricated radial ribs, and rather distinct fine concentric growth lines; radial ribs broader than their interspaces, round-topped and smooth at the upper part of the disc but with growth tend to be accompanied by an imbricated fine radial thread on both sides, and with regularly spaced, more or less lamellated concentric lines; interspaces between radial ribs with fine, somewhat lamellated concentric lines, sometimes with scaled, fine intercalary threads in full adult specimens; scales thin, inclined apically, and regularly spaced; auricles medium in size, anterior one larger than the posterior one, with a deep and wide byssal notch and wide byssal area, and with several, finely scaled radial threads and distinct, somewhat lamellated concentric lines; hinge with distinct but simple cardinal crura, wide and shallow resilial pit with short, widely opening lateral ridges and with conspicuous ctenolium. Left valve moderately inflated, with distinct, more or less squarish, imbricated radial ribs accornpanied by an imbricated, fine radial thread on both sides of the radial ribs towards the ventral margin, imbricated fine intercalary threads and distinct fine concentric lines of growth; radial ribs nearly equal to their interspaces in breadth, flatly round-topped at the upper part of the disc, but tend to become distinctly imbricated ventrally; interspaces between radial ribs with a single or sometimes two imbricated fine intercalary threads which usually appear at about the middle part of disc, and with distinctly lamellated concentric lines; the anterior auricle larger than the posterior one with numerous, finely imbricated radial threads and distinct concentric lines; posterior auricle similar to the anterior one in sculpture. Interior surface gently folded corresponding to radial ribs on the surface and with marginal serration.
Remarks: The type specimens of Yokoyama's species (Geological Survey of Japan) were destroyed during World War II. His specimens were collected from his Upper Byoritz Beds in northern Taiwan, but the exact locality has not been determined. Therefore, the writers find it valuable to describe the detailed characters of satoi based upon a neotype specimen collected from the Toukoushan Formation (Upper Byoritz Beds) at Houlung, Miaoli Hsien. The present species can be distinguished from Chlamys (Mimachlamys) nobilis (Reeve) by its larger number of radial ribs which are accompanied by an imbricated radial thread on both sides and inequivalved shell. Also as pointed out by Masuda, Sato and Shuto (1986) Pecten kakisakiensis described from the Shirahama Formation, Shizuoka Prefecture, Japan (Nomura and Niino, 1932), is a synonym of the present species. The specimens collected from the Miocene and Pliocene formations are generally smaller than the specimens from the Pleistocene formations, though the morphological characters of the shells are quite similar to each other's. *— Neotype; ** — thickness (intact valve)
Type locality: Shihpankeng no. 1, Houlung, Miaoli Hsien (Toukoushan Formation).
Geologic distribution: Toukoushan Formation in Miaoli and Taipei Hsiens; Kueichulin Formation in Taipei and Nantou Hsiens; Choulan Formation in Miaoli Hsien, Taiwan; Dainichi and Shirahama Formations in Shizuoka Prefecture; Tajima Formation in Kagoshima Prefecture; Ananai Formation in Kochi Prefecture; Miyazaki Group in Miyazaki Prefecture; Tomioka Formation(?) in Fukushima Prefecture, and Kume Formation in lbaraki Prefectu¡e, Japan. Geologic range: Late Miocene to 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. 509, 510]
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Chlamys (Mimachlamys) satoi (Yokoyama, 1928); K. Masuda & C. Huang, 1994, Tertiary and Quaternary Pectinidae from northern Taiwan, plate 2, figures 1-7.
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One adult specimen and twelve young individuals were collected. The shell is medium in size, and is almost equilateral except for the auricles. The left valve is more convex than the right. The surface of the both valves is ornamented with 25 to 30 radial ribs which are simple and squarish in the young and become tripartite riblets in the adult stage. Interspaces are narrow and accompanied by an intercalary thread which is imbricated by the concentrical growth-lines near the ventral margin of the adult specimens. Auricles are moderate in size, triangular and ornamented with fine radial threads which make a mesh-like pattern with the growth-lines; the posterior auricle is slightly smaller than the anterior which is low height on the left valve and protrude on the right. The hinge is equipped with a shallow resilial pit and simple cardinal crurae. The byssal notch is wide and deep, and provided with a distinct ctenolium. The interior surface is folded in correspondence with the radial ribs.
This species was originally described by Yokoyama (1928) from the Pliocene Byoritsu Formation of Taiwan, and has been known as a member of the Kakegawa molluscan fauna of southwestern Japan. It has been considered by Masuda (1962) and Masuda et aI. (1986) to be conspesific with Pecten kakisakiensis reported by Nomura and Niino (1932) from the Pliocene Shirahama Formation of Izu Peninsula because of such characters as surface sculpture and an equal number of radial ribs in both species. The senior writer found several specimens, which are assigned to this species, in the upper Pliocene Kurotaki Formation of Boso Peninsula. 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. 488, 489]
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Chlamys satoi (Yokoyama, 1928); S. O'Hara & N. Nemoto, 1988, Pectinids from the Taga Group of the Joban Coalfield, plate 1, figures 4, 5.
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«Comparison:— The present species can be distinguished from Chlamys (Mimachlamys) nobilis (REEVE), a Recent species of Southern Japan, by its larger number of radials which are accompanied by a imbricated radial thread on both sides and inequivalved shell. Pecten kakisakiensis described from the Shirahama Formation, Shizuoka Prefecture (NOMURA and NIlNO, 1932), is a synonym of the present species, because the surface sculpture of both are quite similar to each other and the number of radial ribs of kakisakiensis varies from 25 to 30.
Dimensions (in mm):-- Geologic distribution:— Byoritsu Formation, Taiwan; Nakoshi and Maja Formations, Okinawa Prefecture; Tajima Formation, Kagoshima Prefecture; Takanabe Member of Koyu Formation, Miyazaki Prefecture; Ananai Formation, Kochi Prefecture; Dainichi and Shirahama Formations, Shizuoka Prefecture.
Geologic range:—Pliocene.» SATO, Y., K. MASUDA & T. SHUTO. 1986. Pelecypod fauna of the Shimajiri Group in Miyako-jima, Okinawa Prefecture, Japan. Memoirs of the Faculty of Sience, Kyushu University, [Serie D -Geology], 26 (1): 1-49, pls. 1-5. [p. 22, 23]
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Chlamys (Mimachlamys) satoi (Yokoyama, 1928); Y. Sato, K. Masuda & T. Shuto, 1986, Pelecypod fauna of the Shimajiri Group in Miyako-jima, Okinawa Prefecture, Japan, plate 2, figures 9, 10.
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