Elongated quadrangular, posterior rostrate, sharply truncated and gaping, left valve slightly smaller than right valve, umbones close together, surface of right umbo often eroded or punctured by abrasion against left umbo, thin-walled, surface very finely granular with even commarginal ridges, chalky white, pallial sinus deep, margin smooth. Florida Keys, Gulf of Mexico, Caribbean Central America. Length 20 mm. Note: True T. phaseolina is European, and specimens reported under this name from the western Atlantic belong to an undescribed species (Coan, 1990: 36, 39); no specimens from the western Atlantic have been seen by the authors; the description and figures are based on true specimens from England.