Medium to large size, thin, but strong, orbicular, almost equivalve, slightlt oblique, convex shell. Valves carry approx 20 radial, roundish, regular ribs, about equal in width with the channels in between. Fine riblets in these grooves. valves often covered partly with tiny radially arranged prickles, which some times completely disappear with age. Margins serrated. Ears about equal.

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