The current taxonomy of freshwater mussels (Mollusca: Bivalvia: Unionoida) in the Palearctic (western and northern Eurasia, from Western Europe to Eastern Russia, Korea and Japan) is confused by two competing species concepts: the Biological Species Concept (BSC) and the Comparatory Method (CM). The CM uses the “frontal contour” of the shell as the primary/sole character to delimit bivalve species. Based upon review of the literature, 45 Biological species in 16 genera are recognized in the Palearctic vs. 156 Comparatory species in 34 genera. I argue that the Comparatory Method is typological and that the “species” recognized have no evolutionary or biological basis. The traditional, Biological species are regarded as better representative of actual species diversity, but further revision is required. The problematic legacy of the Nouvelle École on Palearctic freshwater mollusk systematics is discussed.