SNAKES OF THE GENUS PITTJOPHIS 



13 



forms to which they pertain. Individual and sexual variations are 

 summarized in the discussions of the several forms. 



A study of sexual variation, to be significant and undistorted by 

 geographic variation, must include specimens in equal numbers for 

 either sex from a limited area. To illustrate sexual variation in the 

 genus PHuophis a comparative study was made of the scale characters 

 and numbers of spots in 72 specimens of Pituophis catenifer catenifer, 



.120 .130 .140 .150 .160 

 -9 -9 -9 -9 -9 



Figure 9. — Sexual variation in the ratio of tail length to total length in 72 specimens of Pituophis e. catenifer 

 from the vicinity of Palo Alto, Calif. 



36 of each sex, chosen at random from the vicinity of Stanford Uni- 

 versity, Palo Alto, Calif. The results for all characters showing a 

 definite variation are presented diagrammatically in the accompanying 

 graphs (figs. 7-9). 



Variation in number of scale rows. — The dorsal scales are arranged, 

 as stated above, in alternating longitudinal rows, which vary in 



