Abstract
Low quality shells are easily broken, have a high water content and low specific gravity, and contain little pearly and much chalky material. Pearly shell is secreted throughout the season before and after the chalk which it incloses. Chalky areas occur in all shells, have functional importance, are commonest in oysters that are poorest in late summer and are regular in their order of appearance and position on the shell. They are composed of large vertical calcite crystals in a porous mass of smaller crystals with a protein matrix.