Malleus is a genus of hammer oysters (marine bivalve mollusks) in the family Malleidae.

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.

This bivalve-related article is a stub.