DOLPHIN, a name properly belonging to the common cetacean mammal known as Delphinus delphis, but also applied to a number of more or less nearly allied species. The dolphins, bottle-noses, or, as they are more commonly called, "porpoises," are found in abundance in all seas, while some species are inhabitants of large rivers, as the Amazon. They are among the smaller members of the cetacean order, none exceeding 10 ft. in length. Their food is chiefly fish, for the capture of which their long narrow beaks, armed with numerous sharp-pointed teeth, are well adapted, but some also devour crustaceans and molluscs. They are mostly gregarious, and the agility and grace of their movements in the water are themes of admiration to the spectators when a "school of porpoises" is playing round the bows of a vessel at sea.
The Common Dolphin (Delphinus delphis).
The type of the group is the common dolphin (D. delphis) of the Mediterranean and Atlantic, which usually measures 6 to 8 ft. in length, and is thickest near the centre, where the back fin rises to a height of 9 or 10 in., and whence the body tapers towards both extremities. The forehead descends abruptly to the base of the slightly flattened beak, which is about 6 in. long, and is separated from the forehead by a transverse depression. The mouth is armed with sharp, slightly curved teeth, of uniform size, varying in number from forty to fifty on each side of both jaws. The aperture of the ear is exceedingly minute; the eyes are of moderate size and the blow-hole is crescent-shaped. The colour of the upper surface is black, becoming lighter on the flanks, and perfectly white below. Dolphins are gregarious, and large herds often follow ships. They exhibit remarkable agility, individuals having been known to leap to such a height out of the water as to fall upon the deck. Their gambols and apparent relish for human society have attracted the attention of mariners in all ages, and have probably given rise to the many fabulous stories told of dolphins. Their appearance at sea was regarded as a good omen, for although it presaged a tempest, yet it enabled the sailors to steer for a place of safety. The dolphin is exceedingly voracious, feeding on fish, cuttlefishes and crustaceans. On the south coast of England it lives chiefly on pilchard and mackerel, and when in pursuit of these is often taken in the nets. The female brings forth a single young one, which she nurses most carefully. Her milk is abundant and rich, and during the operation of suckling, the mother floats in a slightly sidelong position, so as to allow of the necessary respiration in herself and her young. The dolphin was formerly supposed to be a fish, and allowed to be eaten by Roman Catholics when the use of flesh was prohibited, and it seems to have been esteemed as a delicacy by the French. Among the seafaring population of Britain the name "dolphin" is most usually given to the beautifully coloured fish Coryphaena hippuris - the dorado of the Portuguese, and it is to the latter the poet is alluding when he speaks of "the dying dolphin's changing hues."
Many other allied genera, such as Prodelphinus, Steno, Lagenorhynchus, etc., are also included in the family Delphinidae, some of which live wholly in rivers.
Beside these there is another group of largely freshwater species, constituting the family Platanistidae, and typified by the susu (Platanista gangetica), extensively distributed throughout nearly the whole of the river-systems of the Ganges, Brahmaputra and Indus, ascending as high as there is water enough to swim in, but never passing out to sea. It is about 8 ft. long, blind and feeds on small fish and crustaceans for which it gropes with its long snout in the muddy waters at the bottom. Inia geoffroyensis, the single species of its genus, frequents the Amazon, and reaches an extreme length of 8 ft. It is wholly pink or flesh-coloured, or entirely black, or black above and pink beneath. A third is the La Plata dolphin, Stenodelphis blainvillei, a species about 5 ft. in length. Its colour is palish brown, which harmonizes with the brown-coloured water of the estuary of the Rio de la Plata. See Cetacea.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)