SNAKES OF THE GENUS PITUOPHIS 



39 



others. If, however, affinis is accepted as the central form of the 

 genus phylogenetically, the apparent trends in variation proceed in 



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dcppei 



dtppe 



Figure 22— Variation in number of caudals Figube 23— Variation in number of ventrals 

 in the forms of the de.ppei group. plus caudals in the forms of the deppei group. 



most cases unreversed along the lines of dispersal represented by the 

 deppei, vertebralis, catenifer, and sayi-melanoleucus groups. 



