In the Chinchillas, which form a small family peculiar to South America, the incisor teeth are short; the molars are rootless, divided by continuous folds of enamel into transverse plates, and the two series in each jaw converge towards the front; the zygomatic arch has no angular process on the lower margin; the clavicles are slender but perfect; the fore limbs are small, the hind limbs long; the tail of moderate length or long, and turned up at the end; and the fur is very fine and soft. They are Rodents of moderate size and more or less of Rabbit-like appearance, except that the tail is always elongated and bushy. Of the five known species, four are inhabitants of the mountain regions, and one lives in the plains of the region of La Plata. The latter, the VISCACHA (_Lagostomus trichodactylus_), is a stout-built and almost Marmot-like creature, from eighteen inches to two feet long, exclusive of the tail, which measures from six to eight inches. It has four toes on the fore limbs, and three on the hind feet, the latter furnished with long, compressed, and pointed nails; the muffle is broad and covered with a velvet-like coat of brown hair; the fur, which is soft and moderately long, is of a mottled grey colour above, and white or yellowish-white beneath; on each cheek there is a dark band; a white band crosses the muzzle and runs back on each side almost as far as the eye; the tail is dusky-brown or black. The Viscacha lives on the Pampas from Buenos Ayres to the borders of Patagonia, and where it occurs is generally to be found in great numbers, residing in extensive burrows which it digs for itself in the ground, generally in the neighbourhood of copses, and, if possible, near cultivated fields. Each burrow has a great number of passages leading down to several chambers, in which the Viscachas live in family parties to the number of eight or ten. The Burrowing Owl already mentioned as an associate of the Prairie Dogs of North America, is found about the settlements of the Viscachas, living in their burrows, but it is said that the intrusion of these birds immediately drives out the real owners of the dwelling, as the Owls will not observe those rules of cleanliness which are characteristic of their unwilling hosts. Of course the expelled family has to make itself a new residence, and in this way great stretches of country come to be so undermined that they are dangerous to ride over. According to Mr. Darwin, the most favourite resort of the Viscachas in the neighbourhood of Buenos Ayres are those parts of the plain which, during half the year, are covered with great thistles.