Habitat: Intertidal, shoreline rocks Natural History Notes: Colonies of thousands of individuals can be found in the intertidal. Characteristics: The shell grows to 16 mm and is usually ash-gray to white with bands of brown or black, or mostly black-brown with gray bands. Sometimes shades of orange-brown are present. The operculum is orange-brown, becoming translucent towards the margins, and is round and multispiraled. The apex of the shell is often eroded. Three spiral cords cross coarse axial ribs on each whorl forming small nodules.