Kingdom : Animalia
Phylum : Mollusca
Class : Bivalvia
Order : Euheterodonta incertae sedis
Genus : Polymesoda
Species : erosa
Author : Lightfoot, 1786


Size: Maximum shell length 10.5 cm, commonly to 7 cm.
Color: Outside of shell chalky white under the yellowish green periostracum. Interior chalky or porcelaneous white.
Shell equivalve, subrhomboidal-ovate in outline, slightly inequilateral. Umbones moderately inflated, near the midline of shell. Outer surface of valves concentrically striated. Periostracum thick and strongly wrinkled, the umbones often corroded and showing the shell material. Hinge teeth strong. Anterior and central right cardinal teeth bifid, as well as central and posterior left cardinals. Lateral teeth smooth: 1 anterior and 1 posterior laterals in left valve, against 2 in right valve. Pallial sinus inconspicuous.