1. Potamopyrgus antipodarum. Specimen with spiral keel following the whorls. Keel overgrown with encrustation, so stout shell outline. Aperture closed by operculum. Shell height 4.5mm. Freshwater pool at top of salting, Dee Estuary, Cheshire.
2. Potamopyrgus antipodarum. Specimen with spiral keel following the whorls. Keel overgrown with encrustation, so stout shell outline. Aperture closed by operculum. Shell height 4.5mm. Freshwater pool at top of salting, Dee Estuary, Cheshire.

Potamopyrgus antipodarum. Specimen with spiral keel following the whorls. Keel overgrown with encrustation, so stout shell outline. Aperture closed by operculum. Shell height 4.5mm. Freshwater pool at top of salting, Dee Estuary, Cheshire.