Length 6-9 cm. The Olympia oyster is a small oyster compared to commercial species which can be twice as long. The shell is circular and somewhat smooth. The valves of this oyster are different from side to side (top to bottom). The lower (left) valve is deeply cupped while the upper (right) valve is flat and fits inside the edges of its lower valve. The colour of the outer part of the shell ranges from white to purplish with the inside (nacre) being white to iridescent green to purple in colour. Olympia oysters are often attached by their lower valve to a stationary hard surface but can occur unattached singly or in clusters. Small populations still exist in the Salish Sea (Strait of Georgia) and larger populations are locally common off of Vancouver Island.