- a small clam, Donax variabilis, abundant in the intertidal zone of eastern and southern U.S. coastal beaches, having fanlike bands of various hues, the paired empty shells often spread in a butterfly shape.
- any similar clam, especially of the genus Donax.
- a soft, whitish rock made up of fragments of marine shells and coral, used as a building material.
- a soft limestone consisting of shells, corals, etc, that occurs in parts of the US
