Difficulties in qualitatively identifying Neogene morphospecies of Caribbean Caryocorbula are caused by an interspecific allometric trend that very likely has a genetic basis. In addition, the persistence of this trend through speciation and extinction events, its presence across paleoenvironments, and its resiliency despite sampling effects indicates that the allometry arises from some mechanism of constraint. Based on the strong correlation of Caryocorbula morphology to paleoenvironment, however, selection must still play an important role in the morphologic evolution of this genus.