Shell size to 38 mm; shell heavy, thick, inflated. Sculpture of numerous, low, rounded concentric ridges that are serrated on posterior edge. Lunule heart-shaped with raised lamellae. Color white to cream with irregular brown markings. Internally white, frequently with violet markings. Do not confuse with young southern quahogs, Mercenaria campechiensis, which lack the serrations/crenulations on ridges and are more rounded in outline.