Bivalved mollusks of the superfamily Sphaeriacea (Order Heterodonta) are represented in North America by 34 native and four apparently introduced species of the cosmopolitan freshwater Sphaeriidae and by one introduced species (Corbicula manilensis) of the Afro-Oriental family Corbiculidae. The North American Sphaeriidae include three genera: Sphaerium with 12 species, Pisidium with 25 species, and Eupera with one species. The genera Sphaerium and Pisidium are world-wide in distribution and occur in all North American states and provinces. Eupera is restricted to the Western Hemisphere: northern South America, Central America and the southern Coastal Plain of eastern North America. Although characters of soft anatomy are used in taxonomy of the Sphaeriacea, especially in the classification at the generic level and above, all taxa can be identified readily by characters of the shells, and such shell characters are particularly important in distinguishing the species.