"Shell highly inequivalve, trigonal, pteriform, compressed; test thin; left valve moderately inflated but right valve is nearly flat; hinge-margin straight, almost as long as whole shell-length; anterior margin long, almost straight, forming an angle of 40 degrees or so with hinge-margin; ventral margin short, abruptly curved; posterior one slightly sinuated in dorsal half, forming a small pointed posterior auricle; anterior wing large, elongated along anterior margin, defined from shell-body by an obscure groove in right valve; umbo fairly protruded above hinge line in left valve, but not in right; surface marked with with more or less fluctuated concentric lamellae; inner surface of left valve undulated by some broad radial plications; hinge and ligament structures unknown." [Hayami, 1958 : 163.]
Hayami, 1958: pl. 24, fig. 10 [paratype, MM 2738], 11 [holotype, MM 2737].
"Holotype (MM 2737) Right external mold Length 38.5 mm, height 24.0 mm, thickness 1.5 mm
Paratype (MM 2738) Left internal mold Length 36.0+ mm, height 21.5+ mm, thickness 7.5 mm"
[Hayami, 1958 : 163.]