106 BULLETIN 61, UNITED STATES NATIONAL MUSEUM. 



have the lowest number and Louisiana specimens the highest, which 

 may indicate a tendency toward an increase in tail length in the 

 latter region. 



(6) The number of subcaudals as it is correlated with the tail length 

 is variable, so that the averages in the small series are not to be 

 depended upon. But the largest number occurs in Louisiana and 

 the lowest in the southwestern part of the range in harmony with 

 the variations in tail length. Owing to the correlation of the two, 

 the variation in the latter obscures any tendencies toward dwarfing 

 that may exist. 



(7) The color variations are too slight to permit of the formation 

 of any geographic races on this basis. 



If, then, our material can be relied upon, there is indicated a tend- 

 ency toward a decreased number of dorsal scale rows and ventral 

 plates in southern Mexico and a decreased number of supralabials 

 in general along the Mississippi River, which if true may be considered 

 as an evidence of dwarfing in lyroximnus in these two extremities 

 of the range, while there is an apparent increase in the tail length 

 in Louisiana, as shown by measurements and the number of subcaudal 

 scutes. 



Afinities. — If we admit the evidence of the position of the lateral 

 stripe, 2)roximus is closely allied to sauritus, sackeni, and the members 

 of the Radix group. Its relation to sauritus and sackeni is very 

 close, as will be shown later; but its affinities with the Radix group are 

 less clear. The chief character which separates it from this group is 

 the decidedly longer tail; but, as shown above, the length of tail 

 decreases in the southwestern part of the range, thus lessening the 

 distinctive value of this character. It is in this region, therefore, 

 that the form most closely resembles the forms of the Radix group, 

 and it is here where the closest affinities must be sought. In northern 

 Mexico and western Texas it differs markedly in scutellation from 

 the representatives of the Radix group {megalops and marcianus) 

 only in the smaller number of scale rows (19-17 instead of 21-19-17). 

 This difference, as already seen, is only of racial importance, and as 

 the formula is but one step less than that of the Radix group in this 

 region, there can be no objections on this score to the direct devia- 

 tion of proximus from marcianus or megalops. On the other hand, 

 the range of proximus overlaps the range of marcianus to a consider- 

 able extent without effecting the distinctiveness of either type, 

 which argues against a direct relationship between the two forms, 

 and the same is true of radix. 



Concerning megalops, however, the case is different. The ranges 

 of the two forms come close together in Mexico, but do not overlap, 

 megalops inhabiting the plateau and proximus the coastal plain. 

 The tail length in proximus is also less different from megalops than 



