SNAKES OF THE GENUS PITUOPHIS 133 



Specimens kept in captivity for some time by the writer were well- 

 mannered and could be freely handled without showing resentment. 

 They would eat two or three mice whenever offered, kUling the 

 victim by constricting it, and swallowing it usually head first. The 

 swallowing process, as compared with that of some specimens of 

 Sistrurus catenatus catenatus in a neighboring cage, appeared to be 

 much more efficient and rapid in the gopher snakes than in the 

 rattlers. 



Affinities. — The fact that in scale characters, particularly the shape 

 of the rostral, and in coloration and pattern affinis is the most general- 

 ized form of the genus seems to indicate that it is ancestral to the 

 adjacent forms and represents more nearly than any other form of 

 Pituophis the central form of the genus. Further evidence of this 

 lies in the geographic position of affinis near the geographic center 

 of the genus with several distinct evolutionary lines radiating from 

 it (figs. 18, 33, and 63). Furthermore, in most of the important 

 scale characters and pattern features affinis is intermediate between 

 any two of the forms adjacent to it. 



The reasons for including affinis as a subspecies of sayi rather than 

 of catenifer are given above. 



The probable relationships of affinis and the adjacent forms may 

 be expressed in the following diagram: 



catenifer 

 \ 

 \ 

 \ 

 deserticola 



/ I 



annectens affinis 



(northern) 



vertebralis< affinis >sayi 



(southern) 



deppei 

 Table 11 lists the specimens of this form that have been examined. 



