A rounded to slightly elongated mussel. The posterior end is bluntly pointed in males. Females are shorter and may be nearly square.
The shell is thick, inflated and smooth. Growth-rest lines produce ridges and dark-stained grooves. The outer layer of the shell is yellowish-brown to chestnut-colored in mature individuals. Broad, faint, green rays may cover the shell but are usually absent from adult shells.
Beaks (raised structures located externally near the hinge of the shell) are slightly raised above the hinge line. Beak sculpture, which is often difficult to discern, consists of six to ten fine, wavy, double-looped bars. The teeth (located dorsally within the shell) are large and well developed. The shell's inner lining (nacre) is white to a light salmon or pink and commonly salmon to orange in the beak cavities.