Pseudopotamilla

Key to Pseudopotamilla species described here

1. Collar with high, well-developed, rounded lappets dorsally (Fig. 1 D); dorsal margins V-shaped (Figs 1 D, 2A); and peristomium well exposed dorsally (Fig. 1 D, 1A) and laterally above collar margins (Fig. 2 C)...... P. reniformis (Bruguiére, 1789)

- Collar with low, rounded lappets dorsally (Figs 4 C, 5C); dorsal collar margin convex (Figs 4 C, 5C); and peristomium slightly exposed laterally (Fig. 4 B) or not exposed above collar margins (Fig. 5 B–C)..................................... 2

2. Lateral margins of collar V-shaped (Fig. 4 B); handle of each companion chaeta twice length of handle of adjacent uncinus (Fig. 4 K)........................................................................ P. aspersa (Krøyer, 1856)

- Lateral margins of collar even (in line with the horizontal body axis) (Fig. 5 B); handle of companion chaeta slightly longer than handle of adjacent uncinus (Fig. 5 H)......................................... P. saxicava (Quatrefages, 1866).