The URSON, or CANADA PORCUPINE (_Erythizon dorsatus_), the only North American species of the family, according to Mr. Allen, although other writers distinguish two or three such forms, is about two feet or more in length when full grown, and is covered with woolly hair, and with long coarse hair of a dark brown colour, with the points white or yellowish, this difference in the colour of the tips of the hairs being the chief distinction between the two varieties which Mr. Allen recognises. The spines in both forms are white, with the points usually dusky or brown. The Canada Porcupine is distributed through the whole of the Eastern United States, except on the seaboard, from New York to Virginia, and north of the States through Canada, as far as the limit of trees. The Western Porcupine, which has the tips of the long hairs yellowish (whence it has received the name _E. epixanthus_), occurs west of the Missouri river, extending to the Pacific shores and going southward along the mountains to Arizona and New Mexico, and northwards at least as far as Alaska and Sitka. [Illustration: MEXICAN TREE PORCUPINES.] Although a heavy and clumsy-looking beast, and destitute of the prehensile tail of its South American cousins, this Porcupine is a good climber, and passes nearly the whole of its life upon trees; nevertheless, according to Mr. Allen, it may be met with travelling upon the prairies, probably on its way from one suitable residence to another. On the ground it moves slowly, but its armature of spines is a protection against most of its enemies, and it has the art of striking very forcible and judicious blows with its spiny tail. Audubon and Bachmann mention many cases in which Dogs, Wolves, and even a Puma were found dead or dying in consequence of the severe inflammation caused by the spines of this animal sticking about their mouths; and the former gives an interesting account of a lesson in urbanity given by a captive Urson to a Mastiff that attacked him. The food of the Urson consists of various vegetable substances, fruits, buds, and the young shoots and leaves of trees. In the winter it subsists chiefly upon the bark, which it strips off the upper branches of the trees, and when it has taken up its abode upon a tree it stays there until the suitable bark has been consumed. As it prefers young trees this operation is generally effected pretty quickly, and in this way it is estimated that a single Porcupine may destroy hundreds of trees in the course of a winter. The Urson resides in the holes of trees, and in such situations, or in crevices among the rocks, the female prepares her nest, in which she brings forth usually two, but occasionally three or four, young in April or May. FAMILY XIII.--CHINCHILLIDÆ (THE CHINCHILLAS).