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Class: Bivalvia. 2 specimens. 1 upper (right) valve and 1 lower (left) valve, but the size difference shows not from the same animal as well as both being from different locations. The lower valve is significantly more cupped in shaped than the upper, more flat valve. They are large, white in colour and thick. Both valves have concentric ridges visible but only the lower valve also has radiating ribs. Can be found in shallow coastal waters or estuaries on hard surfaces such as muds and rocks to a depth of approx. 80m. The smaller upper valve found at Saville, Sanday on 28/05/1953. The larger lower valve found at Thieves Holm on 03/09/1958 (this information is written in pencil on the internal surface of the shells).