A good balance is preserved between them all, the result being a high type of pelecypod.
Excepting in a few families, the pelecypod foot is well developed.
When a pelecypod dies and the pull of the adductor muscles is released, the valves gape open.
The greatest possible degree of variation exists in the structure of the pelecypod shell.
In this family we encounter, rather suddenly, some new features not heretofore seen in the pelecypod structure.