Bivalves
those mollusks whose coverings consist of two concave shelly plates or valves united by a hinge. A vast majority of recent bivalve shells belong to Cuvier's testaceous order of ascephalous mollusca, the lamellibranchiate mollusca of Owen, although with them are some classed as multivalves, on account of accessory valves which they possess. There are also mollusks of the class brachiopoda or palliobranchiata, which possess bivalve shells, as the terebratulæ, or lamp shells, etc. A very large proportion of the bivalve shells of the older fossiliferous rocks belong to the brachiopoda.