A solid black shell with a porcelain like green and white operculum (door), which gives the animal it's name. The adults have rounded whorls but the juveniles have three ridges on their whorls which makes them easily confused with other top shells.
Abundant from mid to low intertidal on exposed and sheltered rocky shores.
They feed on filamentous algae and seaweed sporelings
Between the Tides : Bradstock
NZ Coastal Marine Inverts Vol 1