Laevicardium laevigatum Linnaeus, 1758
The Egg (or Egg-Shell) Cockle is well-named, for it is an oval bivalve which might at first glance be mistaken for some sort of egg. The shell is rather thin and well inflated. It may reach a length of three inches. Its approximately 50 fine radial ribs are so delicately etched that they cannot be detected by touch, thus giving the shell's surface a smooth and polished appearance. The inner margin, or border, is crenulate (ridged).
The bivalve shell is white, often tinged or spotted with brownish-orange, yellow or a hint of purple. The shell's thin, gray-brown periostracum is usually worn off when this pretty shell washes ashore. The mollusk lives in sand or mud in shallow water up to a depth of 65 feet. Specimens may be found from North Carolina to Brazil.
An interesting thing about this mollusk is that it has the ability to jump quite well. In fact, a shell collector reports that a live specimen in his boat leapt to freedom.