Noetia ponderosa Say, 1822
This shell is very thick, and heavy for its size. It has distinct radiating ribs (usually around 30) and the rear margin of the bivalve slopes down from the hinge/beak area. The off-center, very prominent beak points toward the rear of the shell. The hinge has comb-like teeth which are visible along the length of the hinge line. The shell may reach a length of 2½ inches. (Looking at the inside of the shell, you will notice that the shape is trapezium-like.)
The ribs may exhibit a bold longitudinal groove (see further information on this “cut-ribbed” feature).
The shell washes up on beaches anywhere from Texas to Virginia and occasionally fossil specimens are found farther north. The non-fossilized specimens are often covered with a blackish-brown felt-like periostracum, though the beak may lack the dark covering.