Gloripallium izurensis Masuda, 1958
MASUDA, K. 1958. On the Miocene Pectinidae from the Environs of Sendai; part 11. Pecten (Chlamys) crassivenius Yokoyama and its related species. Transactions and Proceedings of the Palaeontological Society of Japan [N. S.], 31: 223-229, pl. 32. [p. 227, pl. 32, figs. 4-6]
1958 Gloripallium izurensis Masuda, 1958
K. Masuda, 1958, plate 32.
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«Shell rather small in size, higher than long, rather thin, nearly equivalve, moderately intlated, inequilateral, anterior side a little less than posterior, valves radiately ribbed, and forming an angle of about 85º at apex.
Right valve with six, elevated radial ribs, in which two near submargins are narrower and less elevated than those of central part of disc, a few intercalary threads between the radial ribs, and fine network; radial ribs in the central part of disc conspicuously elevated, round-topped, broader than their interspaces, and divided into several parts with no scales by shallow longitudinal furrows near the beak; divided radial threads on the backs of radial ribs tend to become obsolete downwards, but numerous radial threads appear near the ventral margin; intercalary threads four or a little more in number, appear near the ventral margin and subequal to the divided threads in strength; anterior auricle much larger and longer than the posterior, sculptured with several radial threads and concentric lines, and furnished with deep byssal notch and rather wide byssal area; posterior auricle truncated behind at about right angle, slightly concave downwards, and sculptured like the anterior; hinge with rather distinct cardinal crura, ctenolium, rather wide and shallow resilial pit provided with lateral ridges. Left valve with five, elevated, finely imbricated radial ribs, several intercalary threads between the radial ribs, and fine network; radial ribs narrower than their intcrspaces, divided into finely imbricated, several parts by shallow longitudinal furrows; primary division of radial ribs appears near the beak with fine scales, and further intercalation and imbrication gradually increase towards the ventral margin; several intercalary threads appear near the ventral margin; anterior auricle triangular in form and much larger than the posterior, sculptured with a few radial threads and concentric lines: posterior auricle sculptured like the anterior. Internal surface distinctly folded corresponding to the external sculpture, and with fine serration at ventral margin.
Dimensions in mm: * Holotype. ** Specimen from the Suenomatsuyama formation at Jyûmonji, Tômae-mura, Ninohe-gun, Iwate Prefecture.
Type Locality, Formation and Geological Age:— lzura, Ôtsu-machi. Kita-lbaraki City, Ibaraki Prefecture. Lat. 36º49'06" N., Long. 140º48'02" E. Kokozura formation. Miocene.
Depository:— Holotype, DGS. Reg. No. 3577. Paratype, DGS, Reg. No. 3578. Remarks:— The right valve of this species is characterized by its rather small, moderately inflated shell which is provided with five to six. conspicuously elevated radial ribs which are divided into several parts by shallow longitudinal furrows near the beak, and by the divided threads which tend to become obsolete towards the ventral margin and the numerous divided threads near the ventral margin; left valve by five to six. elevated radial ribs which are divided into several parts with finely imbricated scales. Comparison and Affinity:-- Gloripallium crassivenium (YOKOYAMA), described in earlier pages, is closely related to izurensis, but the latter distinguishable from crassivenium by the small shell, much elevated and less number of radial ribs with no scales, deep byssal notch in the right valve, and in the left valve by the less number of radial ribs which are divided into several parts furnished with finely imbricated scales. Occurrence:— Kokozura formation in lbaraki Prefecture; Ajiri formation in Miyagi Prefecture and Suenomatsuyama formation in Iwate Prefecture: Early to Late Miocene in age.» KÔICHIRÔ MASUDA, 1958
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