tooth shell: see Mollusca.

shell mound, in archaeology, a mound consisting largely of the shells of edible mollusks. It is a kind of kitchen midden found in various parts of the world.

shell money, medium of exchange consisting of shells, the most widely distributed type of ancient currency. Shells are particularly useful as money because they may be strung in long strips of proportionate value or they may be used to provide a single unit value in exchange. Shells ultimately derived their value from their use as jewelry and in rituals. Relative scarcity of the type of shell used or the way the shell is fashioned often determines its value. Cowrie shells have been the most common shell media and are probably the oldest in usage for exchange. Wampum, used in North America, was usually fashioned from thick-shelled clams; dentalia, or tooth shells, were popular with the coastal Native Americans of W North America. Mother-of-pearl and tortoiseshell are said to have been used for trade in ancient China. Oceanic peoples in particular use a variety of shells in trade.

shell, in zoology, hard outer covering secreted by an animal for protection. It is also called the test, crust, or carapace. The term usually refers to the calcareous shells of the many species of mollusk but is also applied to the exoskeleton of the crab and other crustaceans, to the bony covering of the turtle, and to the hard exterior of a bird's egg. People have made use of mollusk shells since early times as receptacles for food and water, as currency (see shell money), and for ornament. The scientific study of shells is called conchology.

lamp shell, common name for animals of the phylum Brachiopoda.

jingle shell: see mussel.

Artillery projectile, cartridge case, or shotgun cartridge. It originated in the 15th century as a container for metal or stone shot, dispersed when the container burst after leaving the gun. Explosive shells, in use by the 16th century, were hollow cast-iron balls filled with gunpowder and lit by a fuse. Until the 18th century, such shells were used only in high-angle fire (including mortars). In the 19th century, shells were adopted for direct-fire artillery, notably in the form of shrapnel. Modern artillery shells consist of a casing (usually steel), a propelling charge, and a bursting charge; the propelling charge is ignited by a primer at the base of the shell and the bursting charge by a fuse in the nose. In rifle, pistol, and machine-gun ammunition, the word usually signifies the brass casing that contains the propulsive charge. In shotgun ammunition, the shell is the entire cartridge, including shot, powder, primer, and case.

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Any of several species of marine clams (family Solenidae) common in intertidal sands and muds, particularly of temperate seas. Razor clams have narrow and elongated shells (shaped like straight razors) up to 8 in. (20 cm) long. A large active foot enables them to move rapidly up and down within their burrow and retreat quickly when disturbed. With their short siphons (tubes) they feed on particulate material in seawater. Some species can swim short distances by jetting water through their siphons.

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