chap, xv.] THE NEARCTIC REGION. 131 



Baird says, that its fauna is almost identical with that of the 

 Gila Eiver, 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 character- 

 istic 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, Iguanidse, Geckotidse, 

 Scincidse, and Zonuridee, appear to be numerous ; and many 

 new genera of doubtful value have been described. Among 

 snakes, Calamariidse, Colubridse, and Crotalidse are represented. 

 Among Amphibia, Siredon, one of the Proteidae, is peculiar. 

 The rivers and lakes of the Great Central Basin, and the 

 Colorado Eiver, contain many peculiar forms of Cyprinidse. 



III. The Eastern or Alleghany Sub-region. 



This sub-region contains examples of all that is most charac- 

 teristic of Nearctic zoology. It is for the most part an undu- 

 lating 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 



