SNAKES OF THE GENUS PITUOPHIS 



101 



the variation in the number of supralabials is very slight, a tendency 

 toward an increase in number from the southern to the central part 

 of the range is indicated, which continues to the northwest, while 

 there is a slight decrease to the northeast. In the preoculars, on the 

 contrary, there is a general tendency to decrease the number from the 

 south to the center of the range, and the decrease is continued to the 



32 



35 



50 



41 



30 



29 



^i^""^^^'"'^"T^^"^n"~^^'X^"~^~ ' 



244 

 242 

 240 

 233 

 •236 

 234 

 232 

 230 

 228 

 226 

 224 

 222 

 220 

 218 

 216 

 214 

 212 



Region T^o, 1 2 3 4 5 6 



FiQTJRE 52.— Geographic variation in number ol ventrals in Pituophis tayi sayi. 



northeastern part of the range, but reversed to the northwestern. 

 The proportionate tail length remains fairly constant throughout the 

 range (fig. 56), tending to increase slightly from south to north, the 

 greatest increase (as also, to a very slight extent, in the caudals, fig. 

 53) appearing in the northwestern part of the range. The variation 

 in the number of body and tail spots (fig. 57) seems to be of little, if 



