(Delphinapterus leucas), also called the "white whale," a cetacean of the family Delphinidae, characterized by its rounded head and uniformly light colour. A native of the Arctic seas, it extends in the western Atlantic as far south as the river St Lawrence, which it ascends for a considerable distance. In colour it is almost pure white; the maximum length is about twelve feet; and the back-fin is replaced by a low ridge. Examples have been taken on the British coasts; and individuals have been kept for some time in captivity in America and in London. See Cetacea.