DOLPHIN, a name for the cetacean Delphinus delphis, and extended to include its allies. The dolphins or porpoises inhabit seas and large rivers. They rarely exceed 1 1 ft. in length. They feed chiefly on fish and are mostly gregarious. They show great agility and grace in the water, and often play round ships. The common dolphin of the Mediterranean and Atlantic measures some 6-8f t. in length, with a back fin of 9 or loin. The "fore head" descends abruptly to the base of the flattened beak, which is about 6in. long. The sharp teeth number some 16o to 200 in all. The eyes are of moderate size, the ear aperture minute, and the blow-hole crescentic. Dolphins are black above, white below. The female brings forth a single young and is a devoted parent.
There are many other genera in the family Delplzinidae, while the Platanistidae include the blind susu (Platanista gangetica) of the Ganges, Brahmaputra, and Indus, and two other species in habiting the Amazon (Inia gcoffroyensis) and an estuary of the La Plata respectively. (See CETACEA.)