VARIATIONS OF GAETER-SNAKES. 



105 



(1) The dorsal scale formula is 19-17 throughout the range, except 

 in southern Mexico, where a specimen with 17-19-17 has been 

 examined. 



(2) The superior labials are 8 over most of the range, 7 only being 

 observed in Yucatan and in general along the Mississippi River. 



(3) The inferior labials are usually 10, occasionally 9 or 11, but 

 the variations are so evenly distributed over the range that no geo- 

 graphic differences can be detected in the small series examined. 



125 



115 

 107 

 99 

 91 

 83 

 75 



Fig. 39. 



-Diagram showing the variation in the number of subcaudal scutes in 

 Thamnophis sauritus proximus. 



(4) The variation in the number of ventral scales is large (150- 

 179), so that from the small amount of material available little reliance 

 can be placed on the averages, but the number (both the averages, 

 maximum and minimum) is strikingly smaller in Veracruz and Yuca- 

 tan specimens than in the series from North America. 



(5) The tail length is very variable, although the mean length for 

 the different localities is quite constant. Southwestern specimens 



