{131}It is a curious fact that the birds of this sub-region should extend across the Gulf of California, and that Cape St. Lucas, at the southern extremity of the peninsula, should be decidedly more "Central" than "Californian" in its ornithology. Prof. Baird says, that its fauna is almost identical with that of the Gila River, and has hardly any relation to that of Upper California. It possesses a considerable number (about twenty) of peculiar species of birds, but all belong to genera characteristic of the present sub-region; and there is no resemblance to the birds of Mazatlan, just across the gulf in the Neotropical region. _Reptiles, Amphibia, and Fishes._--A large number of snakes and lizards inhabit this sub-region, but they have not yet been classified with sufficient precision to enable us to make much use of them. Among lizards, Iguanidæ, Geckotidæ, Scincidæ, and Zonuridæ, appear to be numerous; and many new genera of doubtful value have been described. Among snakes, Calamariidæ, Colubridæ, and Crotalidæ are represented. Among Amphibia, _Siredon_, one of the Proteidæ, is peculiar. The rivers and lakes of the Great Central Basin, and the Colorado River, contain many peculiar forms of Cyprinidæ. _III. The Eastern or Alleghany Sub-region._ This sub-region contains examples of all that is most characteristic of Nearctic zoology. It is for the most part an undulating or mountainous forest-clad country, with a warm or temperate climate, but somewhat extreme in character, and everywhere abounding in animal and vegetable life. To the west, across the Mississippi, the country becomes more open, gradually rises, becomes much drier, and at length merges into the arid plains of the central sub-region. To the south, in Georgia, Florida, and Louisiana, a sub-tropical climate prevails, and winter is almost unknown. To the north, in Michigan and New England, the winters are very severe, and streams and lakes are frozen for months together. These different climates, however, produce little effect on the forms of animal life; the species to some extent change as we go from north to south, but the same types everywhere prevail. This portion of the United States, having been longest inhabited by Europeans, has been more thoroughly explored than other parts of North America; and to this more complete knowledge its superior zoological richness {132}may be to some extent due; but there can be little doubt that it is also positively, and not merely relatively, more productive in varied forms of animal life than either of the other sub-regions.