VAHTATIONS OF tiAKTKH-SNA KKS. 119 



it should be noted lluit sduritus as a form has, exchisive of the dorsal 

 scale rows, a smaller sciitellation generally than either sackeni or 

 'proximus. 



CONCLUSION. 



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

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

 the three forms, proximus, sacJceni, and sauritus, which are apparently 

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

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

 indicate that the three 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 



proximus 



Fig. 51. — rHVLOGENETIC DEVELOPMENT OF THE SaUKITUS GROUP. 



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

 sesses the maximum scutellation (exclusive of the sul)caudal plates) 

 and sauritus the minimum, sackeni possessing an intermediate ntimber. 

 The decrease takes, place gradually from proximus to sackeni to the 

 coastal plain section of sauritus and fi'om proxim^us directly to the 

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

 subcaudal plates increase somewhat from proximus to sauritus and 

 markedly fi'om proximus to sackeni, apparently decreasing again in 

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

 tailed conditions in the trans-Allegheny section of the latter. It must 

 also be stated that according to my observations proximus si)ecimens 

 attain to the largest size. 



The center of origin of this group will be discussed later (see ]). 187), 

 })ut it may be stated here that 1 believe the center of dispersal to 

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

 explanation for its present distribution w^ould seem clear. Being 

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



