Right Valve of Mollusk
Bivalves are molluscs belonging to the class Bivalvia. They have two-part shells, and typically both valves are symmetrical along the hinge line. The class has 30,000 species, including scallops, clams, oysters and mussels. Other names for the class include Bivalva, Pelecypoda, and Lamellibranchia.
The Century Dictionary and Cyclopedia (New York, NY: The Century Co., 1889)