Callinina Thiele, 1931

Examined species: Callinina georgiana (Lea, 1834) (Figs 2C, D, 3C, D, 6C, D); C. intertexta (Say, 1829) (Figs 2E, 3E, 6E).

Remarks: Callinina can be distinguished from Viviparus and the other genera with a concentric inverted-comma-shaped operculum by the following combination of characters: a thin marginal region that obviously differs in colour from the enamel region; a shiny, smooth and relatively small nuclear region; and a narrow inner enamel region.

The only opercular difference found between the two examined species was a relatively darker and thicker operculum in the single examined individual of C. intertexta as compared with C. georgiana .