The lobsters are large ocean-inhabiting crustaceans which are very like the fresh-water crayfish in all structural characters. They live on the rocky or sandy ocean-bottom at shallow depths. They feed largely on decaying animal matter. They are caught in great numbers in so-called "lobster pots," a kind of wooden trap baited with refuse. "The number thus taken upon the shores of New England and Canada amounts to between twenty and thirty million annually." Live lobsters are brownish or greenish with bluish mottling; they turn red when boiled. A single female will lay several thousand eggs. The eggs are greenish and are carried about by the mother until the young hatch. The young are free-swimming larvæ, until they reach a length of half an inch. The shrimps and prawns are mostly marine, though some species live in fresh water. They are, like the lobsters, used for food. Some of the species are gregarious in habit, occurring in great "schools" of individuals. Like the lobsters they crawl about on the sea-bottom feeding on decaying animal matter. Shrimps are very abundant near San Francisco, where extensive "shrimp fishing" is done by the Chinese. [Illustration: FIG. 37.--Some crabs and barnacles of the Pacific coast; the short sessile acorn barnacles in the upper left-hand corner belong to the genus _Balanus_; the stalked barnacles in the upper right-hand corner are of the species _Pollicipes polymenus_; the largest crab (upper left-hand) is _Brachynotus nudus_; the one in left-hand lower corner is a young rock-crab, _Cancer productus_; the crab in the sea-weed at the right is a kelp-crab, _Epialtus productus_, while the two in snail-shells in lower corner are hermit-crabs, _Pagurus samuelis_. (From living specimens in a tide-pool on the Bay of Monterey, California.)]