The DEGU (_Octodon Cumingii_), a very abundant species in Chili, which also extends into Peru, may be taken as a typical example of the whole family, and also of its typical sub-family OCTODONTINÆ, in which the molars are simply indented on each side. The fur is soft, and the tail is short. The Degu is a rat-like animal, rather smaller than the Water Vole, the head and body measuring from seven and a half to eight inches in length, and the tail, exclusive of its terminal tuft, rather more than half that length. The general colour of the animal is brownish-yellow, pencilled with black on the back; the lower surface is yellowish, the feet white, and the tail dusky above, whitish beneath, with the tufted tip dusky or blackish. In the central parts of Chili, according to various travellers, the Degu is exceedingly abundant, living in large societies about hedges and thickets, and running about boldly, even on the high roads. The animals make their burrows in the hedge-banks and similar places, and when alarmed rush into them with their tails elevated, very much after the manner of Rabbits. As the burrows communicate freely with each other, the Degus can easily escape pursuit, going in at one opening and coming out at another at some considerable distance. They sometimes climb up into the bushes among which they live. Their ordinary food consists of the herbage which grows about their dwelling-places, but they also invade gardens and fields, where they may do considerable damage. In the winter they will feed upon the tender bark of certain trees, but they are said by some authors to lay up a store of food against this season. They do not become torpid. The female is believed to produce two broods in the year, each consisting of from four to six young. Two other species of _Octodon_ are known from Chili and Bolivia, which region is also inhabited by two species of _Habrocoma_, a genus distinguished by the large size of the ears, and the extreme softness of the fur. In these animals the molar teeth differ in the two jaws, the upper ones being as simple as in the preceding species, while the lower ones show a complication of the enamel folds like what we shall meet with in the third sub-family. The BROWN SCHIZODON (_Schizodon fuscus_), which inhabits certain elevated spots in the southern part of the Andes (75° S. lat.), has the enamel folds of the molar teeth meeting in the middle. It is about the size of the common Rat (seven and a half to nine inches long), and has a shortish tail clothed throughout with short hairs. Its fur is dark brown above, dirty yellowish beneath. This animal inhabits grassy places near mountain streams, where the ground is sometimes so undermined by its burrows as to render travelling on horseback very uncomfortable. It is a nocturnal animal, and passes most of its life underground. The valleys it inhabits are covered with snow for at least four months in the year.