SOLID ARK Arca solida G. B. Sowerby 1, 1833: 18; Barbatia digueti Mabille, 1895: 72. Shell subquadrate, inflated. Sculpture of fine, closely spaced radial ribs, and commarginal nodes. Periostracum thin, scabrous. Hinge teeth vertical, robust, about 8 anteriorly and 13 posteriorly. Length to 15 mm. San Diego, California (32.7°N) [CAS], within the Golfo de California, to Chimbote, Perú (9.1°S) (Olsson, 1961), from the intertidal zone to 5 m.
Similar to the Atlantic Arcopsis adamsi (Dall, 1886), which is more elongate and has finer sculpture, and to the African A. afra (Gmelin, 1791), which has still finer sculpture and a more keeled posterior end. Although sometimes reported from California based on misidentified specimens of Acar bailyi, it also occasionally reaches those waters.