Campeloma Rafinesque, 1819

Examined species: Campeloma decisum (Say, 1817)

(Figs 2B, 3B, 6B).

Remarks: The elongated, inverted-comma-shaped and concentric operculum is the most important combination of diagnostic opercular characters for Campeloma . The apex–nucleus distance is clearly longer than the base–nucleus distance. This character is seen only in Campeloma and Lioplax, the two extant genera of Lioplacinae .