-ZESgeriidae 
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 
3 So 
