Malleus is a genus of hammer oysters (marine bivalve mollusks) in the family Malleidae. This genus includes 27 known species.
Characteristic of this genus is the unusual "hammer-shaped" outline of the valves. The shells are nearly , 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.