Top: breadth 7.25mm. Small shell: large round umbilicus, but columellar lip already slightly encroaching onto it. Parietal lip reflected as a glaze onto body whorl. Interior thickened by shiny silvery-white aragonite crystals (nacre). Border lacks nacre, coloured as exterior.
Left: breadth 10.8mm. Spiral lines below periphery become concealed by overlapping subsequent whorls. Translucent operculum only showing pale flesh on specimen with little body pigment.
Centre: breadth 12.5mm. Umbilicus constricted into ellipse with growth. Over 13 raised spiral lines on base below periphery, some indistinct.
Right: breadth 14.8mm. Umbilicus often sealed over by columellar lip on large shells, but kept open on this one by occupying, acid-secreting Polydora sp. worm (protruding; gelatinous extension tube removed). Operculum darkened with age, and dark body pigment shows partly enclosing paler opercular disc.
Menai Strait, Wales. February 2014.