Valves of Argopecten gibbus are deep and generally equal, with 17 - 23 (usually 20) deep, radiating ribs (Allen and Costello 1972). The left (upper) valve is somewhat more convex than the right (lower) (Broom 1976). Base color of the shell is creamy white to yellowish, splotched with patches of bright red, maroon, or lavender, with the left valve typically more brightly colored that the right. Wings lateral to the hinge of the shell are equal in length. Calico scallops may reach 2 inches in shell height, and over 3 inches in shell length.