Malleus (bivalve)

Malleus is a genus of hammer oysters, marine bivalve mollusks in the family Malleidae, the hammer oysters. This genus includes 27 known species.

Characteristic of this genus is the unusual "hammer-shaped" outline of the valves. The shells are nearly equivalved, but the hinge line is extremely long and is at nearly a right angle to the rest of the valves, which grow ventrally. The viscera of the organism are arranged in an oval-shaped patch near the umbones of the valves.