Echidna, a genus of primitive mammals, constituting with Ovnithorhynchns (q.v.) the sub-class Prototheria (=z Monotremata = Ornithodelphia). This genus, which has several species, is confined to the Australian region, and owes its scientific name (= viper) to the presence of a perforated spur on the heel, long supposed, but erroneously, to be poisonous, though its function, as well us that of the glands with which it communicates, is unknown. The best-known species, JS. hystrix, from Australia, is about n foot long, and in appearance resembles a hedgehog with a long, naked snout, and strong feet fitted for digging. The ends of the toes of the hind feet turn outwards and backwards when the animal is at rest. Ants are its favourite food, and these are taken with its long protrusile tongue, which is covered with a slimy secretion to which they adhere, and, after being swept into the mouth, they are crushed between the spines' on the palate and tongue. Like the Ornithorhynchus, the Echidna lays true eggs, which are carried in a pouch till hatched. The Tasmanian form, which has the hair sufficiently long to cover most of the spines, is probably only a variety, though some authorities give it specific rank as E. setosa. New Guinea has two forms - E. lawesi, from the neighbourhood of Port Moresby, distinguished by its long cylindrical spines, and the bristles on the face, and E. bruijnii, from the north of the island, with three rows of recurved spines on the tongue, whence it is sometimes made a separate genus (Aeanthoylossns). These animals are popularly known as Porcupine Ant-Eaters.