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 zoogeographical 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 excejpt 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, 0. H., "Distribution of Life in North America," p. 26. 

 t Carpenter, GL H., "Nearctic or Sonoran ?" pp. 5357. 



