20 INTRODUCTION 



The Transition Zone is one of cooler climate. It there- 

 fore occurs on higher levels in the mountains and along the 

 northern coast. 



Owing to the great variation in topography and the in- 

 fluence of a cool ocean current, with resultant winds and 

 fogs, the life zones, particularly in California, often have 

 very irregular outlines. 



Each of these zones may be divided into minor units, 

 technically known as Faunas. These also, doubtless, are 

 dependent for their origin upon certain climatic differences, 

 probably largely of humidity. 



Each of these Faunas is characterized by the presence of 

 certain species which do not live in the others, and the ab- 

 sence of other species peculiar to the adjoining areas. 

 Other species, though not restricted to one, conform more 

 or less closely to the geographical limits of two or more of 

 these life areas. Our knowledge of the distribution of 

 reptiles is still so imperfect as to leave much to be desired. 

 The following lists show, in a general way, the known dis- 

 tribution of the various species and subspecies. The desert 

 is Lower Sonoranj the southern coast and valleys are, in the 

 main, Upper Sonoranj the northern coast and Sierra 

 Nevada are Transition. 



