SNAKES OF THE GENUS PITUOPHIS 



31 



The tail length varies as stated above from 0.114 to 0.157 of the 

 total length. The lowest extreme, found in a specimen from Guana- 

 juato, is considerably below the next higher number, and the average 

 for the form is 0.141. From the graph of this character (fig. 17) it will 

 be seen that it remains fairly constant throughout Mexico and is 

 considerably higher in the California and Texas specimens, indicating 

 a tendency toward an increase in these regions. It must be remem- 

 bered, however, that the California specimen and one of the Texas 



Southe.n Ccniral 

 Mexico Mexico 



Norlhern 

 Mexico 



Figure 13.— Geographic variation in number of ventrals in Pituophis deppei deppei. 



examples are males and would tend normally to have a greater than 

 average tail length. 



Thus, to summarize, we find that the evidence from a consideration 

 of the totality of the characters indicates a dwarfing from north to 

 south, away from the probable center of origin for the form, accom- 

 panied by an increase in the number of spots. 



Sexual variation is evident in many of the characters. Thus, the 

 scale rows in males vary from 26-27-21 to 29-31-21, while in females 



