This order includes two families: the _Ornithorhynchidæ_ and the _Echidnidæ_, both belonging to Australia and Tasmania. The former are aquatic in their habits, the latter terrestrial. The Echidna (_Echidna Hystrix_), or Porcupine Ant-Eater, resembles the Porcupine in his general appearance and coat of spines, the Ant-Eater in his snout, mouth, and long lubricated tongue. His legs are very short and thick, and each is furnished with five broad rounded toes; the four toes are armed with a long blunt claw, but on the hind-feet one toe is without a claw, two are short and blunt, and one is of great length, rather curved, and sharp pointed. He measures about twelve inches, and all over the upper-parts of the body and tail is thickly beset with formidable spines, very sharp and strong; over the head, legs, and under-parts with bristly hair of a deep brown colour. His short tail is covered with perpendicular spines. Digging up the ground with his keen claws he disburies a host of insects, which he rolls over his long red cylindrical tongue. He is very timid, and when any one approaches him, coils himself up in a ball, like a hedgehog. [Illustration: 1. Ornithorhynchus. 2. Echidna.] The _Ornithorhynchus_ ("Bird-beaked"), or _Duck-Billed Platypus_, is another extraordinary animal, which seems to serve as the connecting link between the aquatic birds and the mammalia. His length is about twenty inches; his body, long and flattened like an otter's, is covered with a thick soft fur, moderately dark brown above and whitish beneath; his tail is flat and obtuse; his feet are furnished with a membrane that unites the toes; and he has an elongated, enlarged, and flattened muzzle like a duck's beak. It is evident, therefore, that he can live only on soft food, and that his habits must be aquatic; and hence we find him burrowing in the banks of the streams, and groping for his food, like a duck, among the mud and water. The settlers term him characteristically "the River-Mole." A word of allusion must now be permitted to the _Petrogale_, a genus of the Kangaroo family, described by Dr. Gray. The Brush-tailed Rock Wallaby (_P. penicillata_) has a rough long fur, of a dusky brown hue, tinged with red and gray; a white streak passes down the middle of the throat; his tail is very black, like a raven's plumage, long, and furnished with thick hairs forming a brush. The male is about three feet and a half long. Another species is called the Short-Eared Rock Kangaroo (_P. brachiotis_). Both are excessively wild and shy in their habits, frequenting in the day-time the most inaccessible rocks and the loftiest mountain-peaks, and descending, at the approach of twilight, to feed in the retired and grassy valleys. They flock together in such numbers as to form well-beaten paths along the mountain-sides, and leap from crag to crag with all the agility of the chamois. * * * * *