CHAPTER IX 
SOUTH-WESTERN NORTH AMERICA 
The region to be dealt with in this chapter is of enormous 
extent. To speak of it vaguely as south-western North 
America is apt to give the impression as if only Texas 
and the adjoining western States were being considered. 
What is described here under that designation contains almost 
the whole of the western States with Mexico in addition. 
There is material enough for several chapters. Nevertheless, 
the profound zoogeograpliical importance of this portion of 
North America will be more readily realized, I think, if the 
leading facts are compressed into one brief essay. The Rocky 
Mountain fauna, moreover, which enters largely into the 
south-western region, has already formed the substance of a 
special chapter. 
The term “ Sonoran Region ” was first applied by Pro¬ 
fessor Cope to part of this important south-western life area, 
because he recognised the striking difference it presented as 
compared with other parts of the United States. In one of the 
previous chapters I alluded to the scarcity of lizards in the 
eastern. States in comparison with western Europe. I might 
have said “ western States of North America ” instead of 
western Europe, for lizards especially, and reptile life in 
general, abound in the region we are now considering. 
The term “ Sonoran,”* derived from Sonora, a province of 
northern Mexico, is now often applied to the fauna of the 
whole of North America excejit the boreal portion; and Pro¬ 
fessor Carpenter f supports the contention that the continent 
can be readily divided into two faunistic sections, one of which 
is distinctly autochthonous, the other derived from northern 
Europe and Asia. I have already put forward my reasons for 
* Merriam, C. H., “Distribution of Life in North America,” p. 26. 
t Carpenter, G. H., “Nearctic or Sonoran ?” pp. 53 — 57. 
