30 



BULLETIN 17 5, UNITED STATES NATIONAL MUSEUM 



toward increase from south to north. The infralabials are more 

 variable, 11 being the commonest number, while 12 and 13 are almost 

 equally common. We find only one specimen, from Chihuahua, 

 Mexico, in which there is a decrease to 10, and one specimen each 

 from Tacambaro in Michoacan, Jamay in Jalisco, and San Marcos, 

 Tex., that have 14 infralabials on one or both sides. One specimen 

 only, from Chihuahua, Mexico, varies from the normal in having 2 

 prefrontals on each side instead of 1. The postoculars are more 

 variable, 2 being the commonest number, while nearly as large a 



29-31-22 

 29-31-21 

 27-31-21 

 29-29-20 

 28-29-23 



27-29-22 

 27-29-21 

 27-29-20 



26-29-21 

 25-29-21 

 27-27-21 

 27-27-19 



Southern Central Noittic 



Meiico Meiico Mciic 



Figure 12.— Geographic variation in number of scale rows in Pituophis deppei deppei. 



proportion have 3, and a large number have 3 on one side and 2 on the 

 other. One specimen from Jamay, Jalisco, and the specimen from 

 Real de Finos, Cahf., each have 4 on one side, and a specimen from 

 Ada Magdalena, Durango, has 4 on both sides. These variations in 

 the oculars seem to be of little, if any, geographical significance, and 

 a much larger series of specimens is needed to furnish reUable evidence. 

 The variation in the number of spots seems to be very definitely 

 correlated with the distribution of the form, showing a constant 

 decrease from south to north in both averages and extremes of varia- 

 tion (fig. 16). 



