P. vortex.

P. deformis.

P. contortus.

P. hispidus.

P. nitidus.

P. imbricatus.

P. carinatus. The keeled Planorbis.

Species with a keel; depressed, upper side concave.

P. corneus. The horny Planorbis. Pl. [20], fig. 4.

Species without a keel.