Shell large, up to 78 mm. (3 inches) in length, but usually only about two-thirds that size, ovate, with an almost smooth margin, broadly rounded in profile, depressed to rather tall in fully-grown examples, with the apex varying between the anterior third and subcentral. Sculpture consisting of slightly raised, narrow radial ribs, crossed by weak concentric growth lines; between 50 and 60 radials, including intermediates, in fully adult shells. Colour distinctive; externally greenish blue, with the radial ribs and concentric growth lines picked out in reddish brown, or occasionally in black; internally, bluish silvery, with the external rib pattern showing through; spatula ivory-white but more or less stained orange-red, or sometimes dark-chocolate. Length: 42-78 mm; Width: 32-66 mm; Height: 13-30 mm.

This very attractive species is easily recognised by the orange-stained spatula and by the intricate external pattern of reddish brown radial ribs and concentric growth lines on a greenish blue ground.

Japan, common and widespread.