SNAKES OF THE GENUS PITUOPHIS 113 



Burt (1935b, p. 331) reports finding "on the sunny afternoon of 

 March 29 a number of large buU snakes and several adult blueracers . . . 

 basking on the south slope of a hill . . . Just below the mass of snakes 

 a hole about three inches in diameter extended straight downward 

 for a distance of over a foot and then it zig-zagged through some 

 buried rocks." Most of the snakes escaped into this retreat, and it 

 was assumed that they had been "in this den during the winter." 



Affinities. — Undoubtedly P. sayi sayi is closely related to the 

 neighboring form sayi affinis. The latter is here included as a sub- 

 species of sayi, rather than of catenifer, since it intergrades with 

 s. sayi in northern Mexico, where the two forms can be distinguished 

 only with the greatest difficulty, while it intergrades with none of the 

 subspecies of catenifer; and since it is in both scale and pattern char- 

 acters obviously more closely related to s. sayi than to any of the 

 subspecies of catenifer, or any other forms of the genus. The deriva- 

 tion of sayi from affinis is indicated by the similarity of scale char- 

 acters and pattern of the two forms, particularly in northern Mexico. 

 In these characters affinis is in general intermediate between sayi on 

 the one hand, and the catenifer and deppei groups and vertebralis on 

 the other. 



That sayi is directly ancestral to ruthveni, and thus indirectly to the 

 entire melanoleucus group, is indicated by the similar scale characters 

 of the two forms. Thus, except for the slightly longer rostral, ruth- 

 veni might readUy be confused with sayi in scale characters, although 

 never in coloration. It is noteworthy that in the dorsal scale formula 

 ruthveni more closely resembles the neighboring Texas and Oklahoma 

 specimens of sayi than the more northern specimens with a lower 

 average dorsal scale formula. 



The probable affinities of sayi with the neighboring forms may be 

 expressed by the following diagram: 

 deserticola 



afRnis 

 (northern) 



affinis >sayi >ruthveni 



(southern) 



deppei 

 Table 10 lists the specimens of this form that have been examined. 



