Irregularly quadrangular to oval, with margins often distorted, right valve more inflated than left, umbones slightly anterior, close together, surface of right umbo often eroded or punctured by abrasion against left umbo, thin-walled, with commarginal growth lines, wrinkles, and granules (see inset), and a poorly defined radial ridge separating posterior quarter of valve, chalky white; interior white. North Carolina to Florida, Bahamas, West Indies. Length 15 mm (to 18 mm). Note: Frequently misidentified as Thracia corbuloides Blainville, 1824, a European species.