VARIATIONS OF GARTER-SNAKES. 



27 



Fig. 8." Thamnciphis ordixoides (1109 

 Field Museum), showing third supka- 



LABIAL reduced AND PARTLY FUSED WITH 

 THE FOURTH TO LEAVE SEVEN. 



plate. That fusion also plays a part is also very evident, how- 

 ever, as illustrated l)y fig. 8, but that this usually takes place only 

 when the plate in question has be- 

 come much reduced in width also 

 appears evident, for specimens have 

 not been observed in which either of 

 the adjacent plates were strikingl}- 

 enlarged, as must have been the case 

 had this plate fused mth either of its 

 neighbors before becoming reduced. 

 The fact that the adjacent plates are not noticea])ly larger in speci- 

 mens with 7 than in those ^vdth 8 supralabials also makes it very 

 probable that mth this loss of a supralabial in front of the eye there 



is associated a shortening of the muz- 

 zle. In forms wliich have normalh^ 7 

 the arrangement is exactly the same as 

 in specimens with 7 in the forms wliich 

 have 7 or 8 (fig. 9). 



There is but one form (hutleri) in 

 which the supralabials are very fre- 

 quently 6, but radix (and apparently 

 also ordinoides) occasionally exhibits a tendency to have less than 7. 

 If a specimen of radix or hutleri (fig. 10) with 6 labials be examined, 

 it will be found that the first four scutes are arranged exactly as in 

 specimens with 7 (fig. 7). The fifth plate, however, is somewhat 

 wider than usual, extending to beyond the 

 middle of the first temporal instead of in front 

 of it, while the next, which is now the last, 

 extends to the middle of the third as usual.'^ 

 In hutleri, and frequently in radix, when there 

 are 7 labials the same arrangement of the 

 scutes is adhered to, except that the fifth in 

 these individuals extends from the postocular 

 to a point in front of the middle of the first 

 temporal (its normal position in forms with 7 

 scutes in this series), wliile the next extends from here to beyond the 

 middle of this scute, the last retaining the position which it has in 

 specimens with 6 labials (fig. 11). It would seem from tliis that 

 the decrease in the number of labials from 7 to 6 has resulted from 



Fig. 9.— Thamnophis sirtalis (30820 Uni- 

 versity OF Michigan Museum), show- 

 ing the normal arrangement of the 

 labial scutes when the formula is 



7210. 



Fig. 10.— Thamnophis but- 

 LERi (226 Ruthven Col- 

 lection), SHOWING THE 

 LARGE FIFTH SUPRALABIAL 

 CAUSED BY THE DECREASE 

 IN SIZE OF THE PENULTI- 

 MATE SCUTE AND ITS FUSION 

 WITH THE ANTEPENULTI- 

 MATE LABIAL. 



«In many specimens of hutleri the last labial ends below the single large second 

 temporal, but this scute has very evidently been formed by a fusion of the scales 

 which usually constitute the first and second rows behind the fu'st temporal, so that 

 the relative position of the posterior margin of the last supralabial in respect to these 

 scales is the same as in other forms which do not have a single temporal in the second 

 row. 



