 They are distinguished by having the two halves of the shell be of equal size and shape, but by having the hinge teeth be in a single row, rather than separated into two groups, as they are in the clams and cockles.In 2010 a new proposed classification system for the Bivalvia was published in by Bieler, Carter & Coan revising the classification of the Bivalvia, including the subclass Paleoheterodonta.Superfamilies and families as listed by Bieler "et al".