VARIATIONS OF GARTER-SNAKES. 



23 



can not be sex, for in no instance where large series have been exam- 

 ined has it been possible to detect any correlation between the 

 number of labials and the sex of the specimens. On the other hand, 

 when the racial differences are examined the apparent definite- 

 ness in the individual variation of the upper labials is seen to be 

 extended also to the lower. Thus, in 

 proximus, which as a form has 8, occa- 

 sionally 7, supralabials, and 10, but 

 also 9 or 11, infralabials, the presence 

 of 9 lower labials occurs much less fre- 

 quently than 11 throughout most of 

 the range, while in sauritus, on the 

 other hand, in which the upper labials 

 are 7, occasionally 8, and the lower 10, 

 occasionally 9 or 11, specimens with 9 

 infralabials are much more abundant 

 than those with 11. Sauritus thus 

 exhibits a tendency toward a smaller 

 number of lower as well as upper labial 

 scutes than proximus. Furthermore, 

 where the ranges of these forms meet 

 and the forms intergrade (in Illinois, 

 for example), the specimens appear to 

 be about equally divided in the posses- 

 sion of 7 or 8 supralabials, while the 

 infralabials are normally 10, with the 

 occasional variations 9 and 11 about 

 equally disposed. This at once sug- 

 gests that these variations are geo- 

 graphic. 



It is difficult to demonstrate a geo- 

 graphic variation in the number of 

 labial scutes within the different forms, 

 for the amount of the individual dif- 

 ferences is usually equal to any geo- 

 graphic variations that exist in the 

 same form. This necessitates the ex- 

 amination of large series of specimens 

 to obtain as near as possible the mean 

 number for each locality, for in small 

 series of specimens slight fluctuations in the locality averages, due to 

 the accidental preponderance of specimens with the same number, are 

 sufficient to obscure any geographic trend in the variations. In cer- 

 tain intergrading forms, however, it is possible to show that geographic 

 differences do occur within the form. There is good reason to believe, 



9-10 



8-M 



8-10 



8-9 



7-U 



7-10 



7-9 



7-9 



6-9 



6-8 



Fig. 3.— diagram showing the method 

 of variation in the number of la- 

 bial scutes that results in the 

 formulas characteristic of the dif- 

 ferent forms of garter-snakes. 



