_Mammalia._--Of the family of moles (Talpidæ) we have 3 peculiar genera: _Condylura_, _Scapanus_, and _Scalops_, as well as the remarkable _Urotrichus_, found only in California and Japan. In the weasel family (Mustelidæ) we have _Latax_, a peculiar kind of otter; _Taxidea_, allied to the badgers; and one of the {116}remarkable and characteristic skunks is separated by Dr. J. E. Gray as a genus--_Spilogale_. In the American family Procyonidæ, a peculiar genus (_Bassaris_) is found in California and Texas, extending south along the mountains of Mexico and Guatemala. _Eumetopias_, and _Halicyon_, are seals confined to the west coast of North America. The Bovidæ, or hollow-horned ruminants, contain three peculiar forms; _Antilocapra_, the remarkable prong-buck of the Rocky Mountains; _Aplocerus_, a goat-like antelope; and _Ovibos_, the musk-sheep, confined to Arctic America and Greenland. Among the Rodents are many peculiar genera: _Neotoma_, _Sigmodon_, and _Fiber_, belong to the Muridæ, or rats; _Jaculus_ to the Dipodidæ, or jerboas. The very distinct family _Saccomyidæ_, or pouched rats, which have peculiar cheek pouches, or a kind of outer hairy mouth, consists of five genera all confined to this region, with one of doubtful affinities in Trinidad and Central America. In the squirrel family (Sciuridæ), _Cynomys_, the prairie-dogs, are peculiar; and _Tamias_, the ground squirrel, is very characteristic, though found also in North Asia. _Haploodon_, or sewellels, consisting of two species, forms a distinct family; and _Erethizon_ is a peculiar form of tree porcupine (Cercolabidæ). True mice and rats of the genus _Mus_ are not indigenous to North America, their place being supplied by a distinct genus (_Hesperomys_), confined to the American continent. _Birds._--The genera of birds absolutely peculiar to the Nearctic region are not very numerous, because, there being no boundary but one of climate between it and the Neotropical region, most of its characteristic forms enter a short distance within the limits we are obliged to concede to the latter. Owing also to the severe winter-climate of a large part of the region (which we know is a comparatively recent phenomenon), a large proportion of its birds migrate southwards, to pass the winter in the West-Indian islands or Mexico, some going as far as Guatemala, and a few even to Venezuela.