VARIATIONS OF GAKTER-SNAKES. 119 



it should be noted that sauritus as a form has* exckisive of the dorsal 

 scale rows, a smaller scutellation generally than either sackeni or 

 jproximus. 



CONCLUSION. 



In the foregoing pages we have endeavored to give the results of a 

 study of the characters, habitat relations, variations, and affinities of 

 the three forms, 'proximus, sackeni, and sauritus, which are apparently 

 united into a single group by the position of the lateral stripe upon 

 the third and fourth rows and the long tail. The evidence seems to 

 indicate that the tlu-ee forms intergrade perfectly with each other, but 

 even though the evidence may be considered too slight to prove this, 

 I believe it to be indisputable that the closest relationships of these 

 forms are along the common boundaries (fig. 51). 



sauritus 



sackeni 



proximus 



Fig. 51.— Phylogenetic development of the Sauritus group. 



Of the tlu'ee forms, froximus, in northern Mexico and Texas, pos- 

 sesses the maximum scutellation (exclusive of the subcaudal plates) 

 and sauritus the minimum, sackeni possessing an intermediate number. 

 The decrease takes place gradually fi'om froximus to sackeni to the 

 coastal plain section of sauritus and from proximus directly to the 

 trans- Allegheny section of sauritus. The tail length and number of 

 subcaudal plates increase somewhat from proxinfius to sauritus and 

 markedly from proximus to sackeni, apparently decreasing again in 

 the coastal plain specimens of sauritus, thus approaching the shorter- 

 tailed conditions in the trans-Alleghen}^ section of the latter. It must 

 also be stated that according to my observations proximus specimens 

 attain to the largest size. 



The center of origin of this group wall be discussed later (see p. 187), 

 but it may be stated here that I believe the center of dispersal to 

 be in northern Mexico. If the group did originate in this region the 

 explanation for its present distribution would seem clear. Being 

 rather aquatic in its habits, we would expect the original stock to 



