84 



increased in size but not in number. The head thus has a clean-cut, 

 trim appearance with its well-defined black and white rings, and the 

 latter are nearly always at least a scale and a half wide on the mid- 

 dorsal line. The eastern section, on the other hand, is much more 

 variable, perhaps correlated with the much greater diversity in 

 environmental conditions. Basal shading of the v/hite scales occurs 

 sporadically in all parts of its range, from Tehama County to San 

 Diego. Frequently numerous additional white markings are devel- 

 oped on the head. As already noted, the number and width of the 

 white rings is altered locally. 



In brief, hoylii is characterized east of the Sierras by a high average 

 number of ventrals, by a somewhat greater number of rings, and by 

 constancy in head and body pattern; while west of the Range it is 

 characterized by a lower number of ventrals and a much greater 



Number 



of labials. 



10 



Infralabials 



Supralabials 7 



/.c: 



Shasta San Fresno, Los San Northern Cape 



Co., Fran- Calif. Angeles, Diego Lov/er San 



Calif. Cisco, CaUf. Co., Calif. Lucas. 



Calif. Yuma. Tucson. 



Fig. 19.— Diagram showing geographic variation in numbers of labial plates in Lampropeltis 

 GETULUS boylii, L. g. yumensis, a>td L. g. conjuncta. 



individual and local variation in other respects. It is not considered 

 that these differences are of subspecific value because both sections 

 of hoylii were produced gradually by evolution from the same form 

 and in the same way, and there has been developed no recognizably 

 constant distinction in pattern, but it does seem to support strongly 

 the view that the Sierra Nevada Mountains form a natural barrier 

 that has forced hoylii to develop in two distinct sections and that the 

 Great Valley of California has been entered only from the south. 



Aifinities. — The preceding discussion of the variations and their 

 significance leaves necessary here only a summary of such points as 

 indicate its affinities. 



The eastern section of hoylii is related directly to yumensis, because 

 (1) the distinction in number of ventrals and number of rings is 



