Key to the species of subgenus Unionicola Haldeman, 1842 from China

1. Medial distance between Cx-IV wide, dorsum with two pairs of small platelets in both male and female, lateral projection longer than ventroproximal one on P-4....................................................................... 2

- Medial distance between Cx-IV narrow, dorsum without platelets in female, lateral and ventroproximal projections on P-4 similar............................................................................. U. marginata Jin, 1997

2. Three projections on P- 4 in different length................................................................. 3

- Lateral projection and ventroproximal projection on P-4 similar.................... U. maolanensis Ding & Jin sp. nov.

3. Ventral apodeme of infracapitulum almost straight in female, medial area of acetabular plates (between the two acetabular groups) with two slender inner setae in male................................................................ 4

- Ventral apodeme of infracapitulum bent distally as a hook in female, medial area of acetabular plates (between the two acetabular groups) with one slender inner setae in male................................... U. xishuiensis Ding & Jin sp. nov.

4. The three pairs of inner thick setae on acetabular plates very long, usually over the margin of adjacent acetabulum in female; P-4 slightly longer than P-5 (P-4/P-5 1.15–1.25)........................................ U. crassipes (Müller, 1776)

- The three pairs of inner setae on acetabular plates short, not reached to the neighbouring acetabulum in female; P-4 much longer than P-5 (P-4/P-5 1.42–1.50)................................................ U. suiyangensis Ding & Jin sp. nov.