Taia Annandale, 1918

Examined species: Taia naticoides (Kobelt, 1909) (Figs 4Q, 5Q, 7Q); Taia shanensis (Kobelt, 1909) (Figs 4R, 5R, 7R).

Remarks: Taia can be distinguished from other genera with a concentric inverted-comma-shaped operculum by the following combination of characters: a subcentral nucleus that is very close to the inner margin; a large nuclear region with many fine, dense grains or veins; an inner opercular region completely or partly covered by a rough sandpaper-like layer; an enamel region that is thickened and deeper in colour near the inner opercular region; and a thin, wide marginal region that obviously differs in colour from the enamel region.

The inner nuclear region of T. shanensis is almost completely covered by a thick sandpaper-like layer, which is mostly absent in T. naticoides .