DISTRIBUTION 19 



reptiles, belonging to 58 genera, 20 families, and two 

 orders. Of these, 11 are turtles, 134 are lizards, and 87 

 are snakes. 



While it is probable that the areas occupied by no two of 

 these species have exactly the same geographical limits, yet 

 the ranges of certain species are, in a general way, conter- 

 minous with those not only of other reptiles but of other 

 kinds of animals and plants as well. Thus, if we map out 

 the areas occupied by the different kinds of mammals, 

 birds, reptiles, insects, plants, etc., we find that the boun- 

 daries of the ranges of many species are nearly coincident, 

 so that in one area we have certain genera and species asso- 

 ciated, while more or less closely related kinds inhabit ad- 

 joining districts. From such study of its animals and 

 plants temperate North America has been divided into a 

 number of life zones, each of which may be subdivided into 

 minor areas technically known as Faunas. 



The life zones of western North America, with which the 

 student of reptiles is concerned, are chiefly those now usu- 

 ally called the Lower Sonoran, the Upper Sonoran and the 

 Transition zones. These zones differ in temperature, in 

 vegetation and in animal life. 



The Lower Sonoran Zone in California includes the great 

 desert areas of the southeastern portion of the state, the 

 lower, hotter parts of the San Joaquin Valley, and small 

 areas farther west. This zone also embraces a large part of 

 Arizona, most of Lower California, and parts of Nevada 

 and Utah. 



The Upper Sonoran Zone in California includes the foot- 

 hill regions and lower mountains, most of the valleys west 

 of the Lower Sonoran Zone, and the southern coast and 

 islands. It extends into the northwestern part of Lower 

 California, and reappears in other states where conditions of 

 temperature are similar. 



