The normal range of length of dolphins is from 5 to 14 feet; the larger species, the whales, are considerably longer. Brain weight is between 1600 and 1700 grams in the familiar dolphins, and reaches 9200 grams and more in the whales. The large brain is associated with what, all observers familiar with these animals agree, is a quite considerable intelligence. Here we must pause to make a plea for the proper usage of common names. The term “porpoise” refers to the small, beakless Delphinidae, which have a triangular dorsal fin and spade-shaped teeth. The name “dolphin” embraces all other members of the family, except the larger forms, which are called whales. The porpoises mostly belong in the genus _Phocaena_, the best known species of which, the Common Porpoise (_Phocaena phocaena_), never reaches a length exceeding 6 feet and weighs 100 to 120 pounds. There are some six species. The finless black porpoise constitutes the only other genus with a single species _Neomeris phocaenoides_. All porpoises are dolphins. The Bottle-Nosed Dolphin, _Tursiops truncatus_, is sometimes called a porpoise. This is incorrect. _Tursiops_ is a true dolphin, and should not be called what it is not. Here we shall be principally concerned with the Bottle-Nosed Dolphin and with the Common Dolphin. The Bottle-Nosed Dolphin has a short, well-defined snout two or three inches long, and is characterized by a prominent fin in the middle of the back. Coloration is dark above and light below. Gestation lasts some ten months, birth is monotocous, and the young are suckled for about 18 months. The tail is delivered first, and the infant, about three feet long and weighing about twenty-five pounds, is immediately quite active, though much in need of the care of its devoted mother. The infant will eventually grow to be between 11 and 12 feet in length, and weigh about 300 kilograms. _Tursiops_ has an enormously wide range, being commonest along the Atlantic coast of America, from Maine to Florida, and occurs in the Bay of Biscay, in the Mediterranean Sea, and as far south as New Zealand. The Common Dolphin, _Delphinus delphis_, is readily recognized by its well-defined narrow beak and distinctive coloration. The beak is some 5 to 6 inches narrower and finer than in the Bottle-Nosed Dolphin, and is sharply marked off by a deep V-shaped groove from the low reclining forehead. The Common Dolphin reaches a length up to 8½ feet. Its range of distribution is very wide, for it may be met in any temperate or warm sea throughout the world, and occurs at times in vast schools.