In most families of bivalves , the two valves of the shell are almost perfectly symmetrical with one another along the hinge line , although the placement and shape of the teeth may differ slightly in the left valve and right valve in order for the two valves to articulate properly .
In most families , the two valves of the shell are almost perfectly symmetrical with one another along the hinge line , though the placement and shape of the teeth may differ slightly in the left valve and right valve so the two valves fit together properly .