Note: Information is dated. Do not rely on it.Porpoise. A species of marine fish-like mammal, belonging to the same family as the dolphin, and to the order Cetacea. It is an inhabitant of northern seas, and is familiar on our own shores. It is usually from four to five feet in length, though frequently more. In color it varies, but is mostly of a jet-black tint on the upper surface, merging into pink, mottled gray, or white beneath. The porpoise is compelled continually to seek the surface of the water for breathing purposes; it is then observed rolling over, as it were, and is heard discharging air from the crescent-shaped blowhole on the crown of the head, at the same time taking in a fresh supply at the mouth. Porpoises are frequently observed in great numbers in pursuit of shoals of herring, mackerel, and other small fish, among which, being of an exceedingly voracious nature, they commit sad havoc.