Thick, rounded or squared and inflated shell, with very prominent posterior ridge and lobed posterior margin; pustules (bumps) extend from umbo to posterior ventral margin, increasing in size. Narrow umbo, slightly raised above hinge line. Epidermis is yellowish-green, becomes brown with age; may have randomly scattered dark-green chevron marks. Inside shell has deep beak cavity; pseudocardinal teeth large, grooved and triangular; lateral teeth short, streaked and straight; nacre (lining) white, iridescent posteriorly. The prominent posterior ridge, pustules and knobs make this species easy to identify.