Shell size to 70 mm; shell light, thin but strong. Sculpture of 15-20 strong, rounded, well-spaced concentric ribs and very fine radial lines. Umbones pointing backward. Hemispherical cavities (chondrophores) on both valves house ligament. Color translucent white.

Shell size to 70 mm; shell oval, fragile, thin. Posterior region with characteristic radial ridge. Posterior end beyond ridge gaping, edges flaring. Surface of valves mostly smooth, with fine growth lines. Color white. Rarely found, lives in sand bars and surf zone. The live clam, photographed by Amy Tripp in Kice Island, Collier County, shows the fused siphons that are typical of the families Anatinellidae and Mactridae.