Transposed Hinge Structures in Lamellibranchs

Abstract

In the course of study of a collection of Eocene fossils from Claiborne Bluff, Alabama, the senior author of this paper noticed two valves, one right and one left, of the lamellibranch Venericardia parva Lea, in which the dentition is partially transposed. Subsequently, the authors made an examination of more than five thousand lamellibranch valves, representing both recent and fossil shells, in search of further examples of hinge-transposition. We have found a total number of twenty-six valves exhibiting this variation. Study of these specimens has revealed some hitherto unreported facts regarding the principles of hinge-transposition. Therefore in this paper, we shall describe and discuss these specimens, and shall present such conclusions as seem justified by the data assembled. Citations to the literature are made by author, date, and page, referring to the list at the end of the paper.