ABSTRACT
Matsukuma (1996) described various bivalve taxa, both modern and ancient examples as far back as the Devonian and Permian, in which the hinge-line structures of the left valve have been transposed to the right valve and vice versa, with the additional complication in some taxa that not every feature of the hinge line need be transposed. This may be a genetically controlled developmental feature, although in the absence of experimental work on living bivalves it is difcult to evaluate the possibility. Cox (1969) discussed transposed bivalve hinges in some detail. Weaver (1963) described an Oligocene Crassatella from California with a transposed hinge. In the same vein is hinge transposition in various bivalves which involves different hinge-line elements, with rst evidence involving Permian taxa. Boyd and Newell (1968) discussed Permian examples and cited a number of younger examples.
