See text Tropidiscus Stein, 1850 Planorbis is a genus of air-breathing freshwater snails, aquatic pulmonate gastropod molluscs in the family Planorbidae, the ram's horn snails, or planorbids.

All species in this genus have sinistral or left-coiling shells.

[2] Planorbis shells are flat-coiled and sinistral.

This genus has a worldwide distribution.

It is known from the Jurassic to the Recent periods.