Tchangmargarya He, 2013

Examined species: Tchangmargarya yangtsunghaiensis (Tchang & Tsi, 1949) (Figs 2N, 3N, 6M); Tchangmargarya multilabiata (Zhang & Chen, 2015) (Figs 2M, 3M, 6N).

Remarks: The two species of Tchangmargarya examined show the largest opercular differences within one genus of Viviparidae . This is especially true of the position of the nucleus. Nevertheless, these two species can still be assigned to a single genus and distinguished from other genera with a concentric inverted-comma-shaped operculum by the following combination of characters: a nuclear region with many grains or veins, an enamel region that is thickened near the inner opercular region and deeper in colour, and a thin marginal region obviously differing in colour from the enamel region.

The operculum of T. multilabiata is obviously different from that of T. yangtsunghaiensis . In the former, the nucleus is positioned close to the inner margin and inner opercular region is larger; while the outer inner and upper inner margins of T. yangtsunghaiensis are inwardly curved, in T. multilabiata only the upper inner margin is inwardly curved.