Viviparus Montfort, 1810

Examined species: Viviparus viviparus (Linnaeus, 1758) (Figs 2I, 3I, 6I); V. contectus Millet, 1813 (Figs 2J, K, 3J, K, 6J, K).

Remarks: Viviparus can be distinguished from the other genera with a concentric inverted-comma-shaped operculum (especially Callinina) by the following combination of characters: a thickened marginal region, obvious concentric growth grooves on the interior surface, a wide inner enamel region, and a small and smooth nuclear region.

The operculum of V. contectus differs from that of V. viviparus in having a thicker marginal region and more obvious grooves.