Interior colours obscured by opaque white or cream porcelaneous layer on large specimens; probably deposited when growth ceases. Amphora area (1) delineated by the anterior mantle-attachment scar (3) and horseshoe shape, translucent scar, ‘myostracum’ (2), left by pedal retractor muscle. Silver vertex patch (4). Top left: tall narrow shell from dry rock near high water mark results from contraction of muscle pulling in the shell-forming mantle while clamping down to resist desiccation during long emersion. Lengths 35, 41 and 42 mm. Anglesey, Wales. March 2014.