626 THE AMERICAN NATURALIST [Vol. XLVH 



On the assumption that the belly scales and body 

 vertebrae are the same, Bateson (1894, p. 123) has pointed 

 out that there must be considerable variation in the num- 

 ber of vertebrae in this region, and Kuthven (1908) has 

 shown that if the number is the same in both series in the 

 genus Thamnophis closely related species when differing 

 in relative size also differ in the number of body and tail 

 vertebrae, since they do so vary in the number of scutes. 



In view of the fact that there may be a discrepancy in 

 the number of vertebrae and ventral scutes, general con- 

 clusions based on the correlation between the two series 

 are of little value until the method, amount and place of 

 variation has been determined. As is well knpwn a pro- 

 nounced sexual variation in the scutes occurs in at least 

 some species, the males having on the average fewer 

 belly scutes and more subcaudal scutes than the females. 

 It might very well be that while the total numbers of 

 scutes and vertebrae are not the same, the number in each 

 whole series is about the same in the two sexes, the varia- 

 tion simply affecting the relative number on the body and 

 tail, or there may be more or less scutes than vertebrae on 

 the body and less or more scutes than vertebrae on the tail, 

 so that the total number in the two series is close together, 

 or the number of scutes may vary independently of the 

 vertebrae sufficiently to bring about the observed sexual 

 differences, the number of vertebrae remaining the same, 

 and the relation between the number of members in each 

 series may be different in different forms. 



It has been the purpose of this study to determine the 

 correlation that exists between the number of belly scales 

 and body vertebrae and between the number of subcaudal 

 scales and caudal vertebrae in two species of snake, and 

 from this to discover if the sexual and individual differ- 

 ences in scales are associated witli differences in the total 

 number of vertebrae or are merely in the relative number 

 on the body and tail. 



The results embodied in this paper were in part ob- 

 tained by Mr. Charles Obee, in 1910, under the direction 

 of the senior writer, and were submitted by him in the 



