Entolium ikedai Tashiro, 1990
TASHIRO, M. 1990. Bivalve fauna from the Kesado formation of Yatsushiro Mountains in Kyushu. Memoirs of the Faculty of Science, Kochi University [Series E - Geology], 11: 1-22, pls. 1-3, text-figs. 1-12. [p. 8, pl. 2, figs. 1-5, text-fig. 5]
1990 Entolium ikedai Tashiro, 1990
M. Tashiro, 1990, plate 2.
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«Material: — Holotype, KSG 5031, external and internal moulds of left valve; paratype, KSG 5032, external and internal moulds of left valve; both from north of Shimofukami, Yatsushiro area, Kumamoto Prefecture.
Diagnosis: — Shell large, subovate, taller than length; anterior and posterior wings nearly symmetrical; umbo less prominent, located nearlycentral; surface with very fine concentric riblets.
Description: — Shell large, subovate or raindolop-like outline except for subtrigonal anterior and posterior wings (ears), higher than length, nearly equilateral, equivalve, slightly intlated; umbo less pronlinent, pointed nearly central of valve; umbonal angle with about 90º; anterior and posterior margins nearly straight; ventral margin semicircle; flank with very fine, abundant, regularly spaced concentric striae or riblets; anterior and posterior wings with numerous, very fine, delicate subvertical threads; anterior wing somewhat larger than posterior one; both lateral sides of the wings subvertical; hinge margin nearly straight; inner margin smooth; inner surface smooth; hinge plate well arched, rather solid, supported by two weak, anterior and posterior, radial buttress, ligament pit very small under beak; three pairs of clule on inner surface of both lateral wings or hinge plate; one pair of ligamental clule short but strong, located at anterior and posterior lateral sides of ligament pit; next pair of clule small, located radialy on both outsides of ligamental clule; marginal clule very weak, elongated subhorizontaly under hinge margin.
Observation: — The concentric ornamentation on the flank are striated delicately and crowded on the umbonal part, but gradually changing into distinctly round-topped riblets according through the growth. An inner radial buttress is low and blunt on the top, but distinctly running from umbo towards postero-ventral margin.
Comparison: — This is closely similar to Entolium sanchuense Hayami (1965), from the Ishido Formation of central Japan, in its delicate concentric sculupture, but differs clearly in its narrower umbonal angle and taller valve than those of E. sanchuensis. Since Entolium tosaense Tashiro et Kozai (1986), from the Monobe Formation of the Monobegawa Group, is characterized by smooth surface, the discrimination between E. tosaense and this species is very easy.
Occurrence: — Loc. 2.»
MASAYUKI TASHIRO, 1990
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