PORPOISE. Any small or moderate-sized cetacean is usually called a porpoise, but the name is applied chiefly to members of the fam ily Delphinidcr, belonging to the suborder Odontoceti, or the toothed whales. Its principal characters are as follows: The anterior pairs of ribs are joined to the vertebrae by both a tubercle and a head. The sternal ribs are com pletely ossified. The cervical vertebra are more or less united. In the skull the pterygoid bones are inflated. The symphysis of the man dible is short. The teeth are always present, but vary greatly in number in different genera; they usually occur in both jaws and are simple and conical. The genus Grampus is without teeth in the upper jaw, and the genus Monodon with out teeth in the lower jaw. The blowhole is single and crescentic in form.
Between 60 and 70 species of porpoises are known, representing 19 genera. They are greatly diversified in form and color. Some have a large, falcate dorsal fin, while in others the fin is reduced in size, or is represented only by a low ridge, or is entirely absent. The pec toral fins are equally varied in size and pro portions, being short and broad in some forms and very long and narrow in others. The beak may be long or short, compressed or depressed, and is sometimes replaced by a narrow rim, or is absent altogether. The representatives of several genera of porpoises have received special names, such as killers (genus Orcinus), grampuses (genus Grampus), blackfish (genus Globicephalus), beluga or white whale (genus Delphinapterus), narwhal (genus Monodon), etc.
The Delphinitice are chiefly marine, but some species of the genus Sotolia live in the Amazon River, and in the rivers of China, and one species of the genus OrciteIla in the Irawadi River, Burma. The harbor porpoise (Phoccena phoccena) and the bottle-nosed porpoise (Tur siops truncatus) frequently ascend the Potomac, Hudson and other rivers of the eastern coast of the United States, and the beluga ascends the Saint Lawrence regularly every spring in large numbers.
The geographical range of the porpoises as a group extends over all seas from the Arctic to the Antarctic, but while some species, such as the common dolphin (Delphinus delphis) have a very wide distribution, that of others is more circumscribed. Thus, the narwhal is confined to the Arctic Ocean, and rarely leaves the ice. The beluga is also an Arctic species, though it ranges southward regularly in spring to the Saint Lawrence, as already stated, and occasion ally individuals stray as far south as Cape Cod and the New Jersey Coast. The white-lipped porpoise (Lagenorhynchus albirostris) is com mon about the British Isles, but is not found on the coast of the United States. The species of
blackfish (GlobicePhalus melas) found on our east coast north of New Jersey is different from that occurring further south. Our commonest east coast porpoise (Tursiops truncatus) is not found in Greenland waters, while the harbor porpoise (Phoccena phoccena), which is abun dant in the gulf of Maine and northward, does not range south of New Jersey. Many species occurring in the tropics and the south seas are never seen in North American waters.
The majority of porpoises feed upon fish, but the various species of blackfish, the nar whal and the white whale subsist chiefly or ex clusively upon cuttlefish, while the killers de vour the young or other cetaceans and of vari ous amphibious mammals, such as seals, sea lions, etc. The stomach of a porpoise (Sotalia teiiscii) recently discovered on the west coast of Africa was found to contain leaves of the mangrove tree and other vegetable matter. Porpoises are gregarious animals, congregating in large herds or "schools," which sometimes comprise an enormous number of individuals. Schools of blackfish numbering hundreds of individuals occasionally approach the land at the Faroe Islands, the Orkney Islands, Cape Cod, and other points, where they strand, or are driven ashore by the fishermen. They are the source of a considerable profit, on account of their oil, which is of a superior quality. The skins of the blackfish and of the white whale are valuable for leather, but the dermis of the majority of porpoises is too thin, or too irregu lar in texture, to form good leather.
Besides the porpoises of the family Delphini der, there are a few species generally called river dolphins representing three genera, which belong to a separate family, the Platanistiche. The best known are the susu of the Ganges River, genus Platanista, a blind form which sub sists chiefly upon fresh-water crustaceans; the inia, genus inia, of the Amazon River; and the Pontoporia, found about the mouth of the La Plata River. These porpoises are remarkable for their long beaks, their broad pectoral fins, their free cervical vertebra, and their rugose or otherwise peculiar teeth. are regarded as highly specialized forms of ancient origin. Nu merous fossil species of DelPhintdce and Platanisticke occurs in the Tertiary and latter geological formations, beginning with the Mio cene. Consult Beddard, F. E., (A Book of (London 19001; Goode, G. B., 'Fish ery (Washington 1884); True, F. W., of the United States National Museum, No. 36) (Washington 1889).