/Bgeriidae 



We detect here the influence of warmer skies and the life of the 

 not-far-off tropics. It is the region of the long-leaved pine, the 

 cypress, the live-oak, the evergreen magnolia, and the palmetto. 

 It is the subregion of the Gulf. It has a fauna of its own. 



In the extreme southern portion of Florida and on the out- 

 lying islands we find established a northern offshoot of the plant- 

 life and of the fauna of the West Indies. The conditions are dis- 

 tinctly tropical here. 



A sharp division takes place west of the Mississippi River, at 

 those points where the heavily wooded lands terminate and are 

 succeeded by the grassy, woodless plains, which lie between the 

 western borders of the Valley of the Mississippi and the eastern 

 ranges of the Rocky Mountains. While the Great Plains are 

 traversed by numerous river valleys, in which there is abundant 

 arboreal vegetation, nevertheless the whole region in part only 

 preserves the faunal and floral characteristics of the Appalachian 

 subregion. The southern part of this territory, lying in New 

 Mexico, western Texas, and Arizona, with which, in part, south- 

 ern California is identified, has a large number of genera and 

 species which range southward along the plateaus and treeless 

 highlands of Mexico and Central America. This may be called 

 the Arizonian or Sonoran subregion. 



The northern half of the belt of the Great Plains is invaded by 

 forms of both plant and animal life which are related to types 

 predominant in the colder regions of the continent. This is 

 especially true where the plains reach a great altitude above the 

 level of the sea. This subregion may be called the Dakotan. It 

 stretches from northern Colorado northward to the British 

 provinces of Assiniboia and Alberta. 



West of the Great Plains is a territory traversed from north to 

 south by the ranges of the Rocky Mountains, in which there 

 occurs a commingling of genera and species, some coming in 

 from the far north on the higher ranges, others coming in from 

 the south on the lower levels, and a multitude of forms mingling 

 with these which show the influence of migration both from the 

 Great Plains and from the Pacific slope. The region of the 

 Rocky Mountains is a region in which there are singular com- 

 plexities, owing to the great differences in elevation. Species of 

 the arctic zone may be found having their habitat within a few 



3S9 



