Small, oval, translucent, horn-coloured operculum has distal (outer) surface of conchiolin with concentric growth rings round peripheral nucleus (1). Proximal (inner) surface has matt surface, where opercular disc attaches (2), with concentric lines running transversely to exterior growth lines. Exposed unattached part of proximal surface is of varnish without growth lines (3). West Anglesey, Wales. March 2014.