VARIATIONS OF GARTER-SNAKES. 67 



in the light of our knowledge of the method of variation and of 

 geographic probability. 



The only character, so far as I can see, that would justify an 

 attempt to derive this form from parietalis and relate it to eques is 

 the pallid color. In general the ground color is nearly the same as in 

 eques, while the paleness of the labials and stripes, and the similarity 

 in the arrangement of black markings, is so close as to result in 

 frequent confusion. Color, as we have seen, is the least important 

 of our criteria, but it is worthy of note that in spite of the pallidness 

 in eques the lateral stripe is always distinctly on the second and third 

 rows throughout the entire length (instead of on the third row only), 

 even in the region in which it occurs with marcianus. In scutellation 

 there is very little resemblance between marcianus and parietalis 

 or eques. The latter in Texas has mostly 8 supralabials and always 

 19-17 scale rows, and parietalis has usually 7 supralabials antl always 

 19-17 scale rows. According to our observations on the variation 

 in the number of scale rows, marcianus could have been derived from 

 either parietalis or eques by an increase in the number of scales, but 

 the further difficulty presents itself that both of the latter species 

 (especially eques) overlap the range of marcianus considerably with- 

 out effecting the purity of the types, and the only way by which they 

 can be considered akin is to invoke the aid of some form of isolation 

 (ecological or physiological), which the evidence t)f similarity does 

 not call for. The difhculty of adopting such an explanation would 

 be less if there were any signs of intergradations in these forms; but, 

 as it is, marcianus has constantly 21-19-17 rows and eques and 

 parietalis 19-17. Its relation to the Elegans group is not, however, 

 so easily disposed of. 



In the possession of 21-19-17 scale rows and 8 labials marcianus 

 agrees closely with Tiammondi and elegans, and while the number of 

 ventral and subcaudal plates is normally less and the tail shorter, the 

 inference might well be drawn that the similarity is an expression of 

 relationship. Nor does the lateral stripe confute this, for it is the 

 general pallidness of the ground color that apparently makes the 

 stripe indistinct except upon the third row. Geographically also it 

 seems, at the fu^st glance, as if this relationship was confirmed, for 

 the range of hammondi, elegans, and marcianus seem to be exactly 

 contiguous, and do not overlap. There are certain facts, however, 

 that confute the evidence furnished by the similarity in scutella- 

 tion. First and foremost, is the lateral stripe to be considered as 

 being upon the second and third rows? Secondly, hammondi is 

 markedly distinct in color from marcianus even in the regions where 

 they approach each other, and this distinctness is supported by the 

 general topography of the body, as expressed in a longer, narrower 

 head, increased number of urosteges, etc., and the presence of two 



