896 The American Naturalist. [November, 
ary crosses Missouri, extends south along the southern bound- 
ary of high lands of Texas, and reaches the Gulf at the mouth of 
the Rio Grande. The Eastern subdivision is the most extended, 
reaching from the isothermal line of 77° F. north and from the 
Atlantic Ocean to the elevated plains west of the Mississippi 
River. Many of its forms extend up the bottoms of the rivers 
which flow to the eastward through the plains. The Sonoran 
subregion extends from the limit of the Eastern as far west as 
the Sierra Nevada, and south, including Nevada, New Mexico, 
Arizona, Sonora and the Plateau of Mexico, including the 
State of Chihuahua, and, perhaps, Durango. It does not cross 
the Sierra Nevada, but includes the entire peninsula of 
Lower California. It extends northward on the east side of 
the Sierra Nevada as far as, including the arid region of 
British Columbia. It occupies the valley of the Rio Grando, 
and extends into Texas as far as the Rio Pecos. It extends 
southward in western Mexico as far as Mazatlan. The Western 
subdivision extends from the Pacific coast to the Sierra Nevada 
to an uncertain distance on the Lower Californian Peninsula. 
At the north it crosses the Sierra Nevada, skips the narrow 
strip of the Sonoran in Washington, and extends to the Rocky 
Mountains, including northern Idaho and western Montana. 
The Toltecan subregion includes the States of Guanajuato, 
Mexico, and the adjacent elevated regions of Michoacan, 
Oaxaca and Puebla, including the Alpine regions of the south- 
ern Sierra Madre. It is probable that another subregion should 
be added, the Tamaulipan of Townsend. This is a dry region 
extending from near the mouth of the Rio Grande to the Rio 
Soto la Marina in the State of Tamaulipas. More information 
regarding the fauna of this country is desirable. 
The faunal peculiarities of these subregions are well marked. 
The three subregions included in eastern North America differ 
from all the others in the abundance of their turtles and the 
small number of their lizards. Prolific of life, this area is not 
‘subdivided by any marked natural barriers. Hence, though 
its species present great varieties in extent of range, it is not 
divided into districts which are very sharply defined. The 
warmer regions are much richer in birds, reptiles and insects 
