The outer hard covering of certain molluscs, turtles, etc., which is used for various purposes, including making or decorating certain objects of jewelry. The shell of molluscs is generally referredto, when applied to objects of jewelry (e.g. brooches and finger rings), as 'shell', but that of turtles as tortoise shell. Shell is sometimes carved as a cameo.The shell of the pearl oyster and other molluscs, the lining of which is nacre (from which articles ofmother-of-pearl are made).