4:50 CRAB a very large and massive species (menippe mer- cenaria), with the body often five or six inches across, is caught in great numbers for the mar- ket. In tropical countries very numerous spe- cies, and among them many land and fresh- water ones, are much used as food. The sand crab, or swift-footed crab (ocypoda arenaria) and the fiddler crabs (species of gelasimus) are among the most highly developed species. The sand crab is almost exactly the color of com- mon beach sand, has a nearly square body, often two inches or more across, long legs, and short claws, nearly alike on the two sides. It is found from New Jersey to Brazil-, and closely allied species of the same genus are found upon the west coast of Central and South America and in the old world. Our species digs deep holes in sandy beaches just above high-water mark, and when overtaken away from its hole runs so swiftly over the sand that it is difficult to catch. It is carnivorous, catching beach fleas, &c., or feeding upon fish or other dead animals thrown upon the shore. Although the adults are almost entirely terrestrial, the young Fiddler Crab (Gelasimus vocans). as soon as hatched swim freely in the water until, in the megalops stage, they are fully a fourth of an inch across the body, but still very unlike the adult.' In this stage they are often thrown upon the beaches as far north as Block island. After coming upon the shore they bury themselves in the sand, and prob- ably soon after change to the adult form. The fiddler crabs are more abundant in sheltered situations, especially on salt marshes ; they are found upon the coasts of nearly all the warmer countries, and three species are common from Cape Cod to Florida. Our species are all much alike, and are at once distinguished by the males having one of the claws, sometimes the right, sometimes the left, enormously develop- ed and much larger than the whole body, while the claw upon the other side is- very small, as both are in the female. They dig holes some- what in the manner of the sand crabs, but usually between tides, and the males run over the shores and marshes, holding up the big claw in front of them in a threatening man- ner. This way of carrying the big claw has probably given rise to the common name. The little oyster crab (pinnotheres ostreum) is found wherever oysters occur on our coast. The female lives, at least when mature, within the shell of the oyster, in the gill cavity. The males are much smaller than the females, being no larger than a small pea, and are rarely if ever seen within the oyster, but are sometimes found swimming at the surface of the water. Other similar species live in many kinds of bivalve shells, and an allied species, found upon the west coast of South America, lives inside a sea urchin or echinus. The spider crab (li- binia canaliculata) of our Atlantic coast has a somewhat pear-shaped body and exceedingly long legs, often spreading more than a foot across, and is always covered with mud, bar- nacles, and other foreign substances, which tend to conceal it from its enemies. It is a representative of a very large class of crabs, some of which are among the largest known. One of them, a species of macrocheira, found in Japan, sometimes measures 10 ft. across the expanded legs. The land crabs (species of ge- carcinus and other allied genera) have the gills so constructed that they are able to live for a long time away from the water, and are even found high up upon mountain sides. They are said, however, to journey to the sea once a year, probably for the purpose of deposit- ing the eggs. Among the anomurans there is even a greater diversity in form and habits than among those previously mentioned, but the spe- cies are not so numerous or important. The her- mit or soldier crabs are the most familiar and widely distributed of the group, numerous spe- cies being found from the Arctic ocean through- out the tropics. Their peculiar habit of living in the spiral shells of mollusks has long attract- ed attention. The shells which they inhabit are often covered with hydroids or other for- eign substances, and some species always have Hermit Crab and Actinia. an actinia upon the shell. The hind part of the body and the abdomen are soft, protected only by a thin integument, and the abdomen is one- sided and curved spirally, so as to fit the shells which they always inhabit and drag about with
