68 BULLETIN 61, UNITED STATES NATIONAL MUSEUM. 



preoculars. Very cvitlently it seems to us that if we grant a relation- 

 ship between these forms it must be a distant one, for there can be 

 no question as to their distinctness at present. 



As regards elegans, the geographic probabiUties may also be con- 

 ceived as favoring a close relationship, for it seems very evident that 

 in Arizona, New Mexico, and Texas, where the range of the two 

 forms come together, elegans is restricted to the plateaus and mar- 

 cianus from them, and the differences between the two forms maybe 

 explained b}^ this separation of their respective ranges and as the 

 result of the different conditions to which they are exposed. Thus 

 elegans, even in the most southern localities from which it is known, 

 San Ildefonso, New Mexico, presents so often a scale formula of 

 19-21-19-17 as to indicate plainly a tendency toward a reduction 

 in scutellation, which may possibly be correlated with the higher 

 altitude of its habitat, while in coloration it resembles so closely dark 

 specimens of marcianus as to make it diflicult at times to refer 

 specimens to the proper form. Furthermore, the generally light 

 color of marcianus, as I have shown, may be correlated with 

 the aridity of its habitat. What, then, is, the objection to this 

 attractive view? If we take for granted that elegans is a dwarfed 

 form of a stock that possessed a larger number of scale rows, it seems 

 to us that we have reason to expect that correlated with the decrease 

 in the number of scale rows there at least will not be an increase in 

 the number of ventral plates, although the tail length and urosteges 

 may vary independently, as we have seen. If the reduction in the 

 different series of scales on the body is correlated, as seems to be the 

 case, then elegans lias apparently been derived from some stock with 

 a larger scutellation than marcianus , since it has a decidedly larger 

 number of ventral plates. This problem will be taken up again 

 when the Elegans group is considered, but it seems to me, although 

 the material is as yet much too meager to warrant any decided 

 opinion, that the neighboring species of the Elegans group all give 

 evidence of being derived from a different source than marcianus, 

 and the opposite. 



If this point be granted, I have now excluded marcianus from all 

 except the Radix group, and it remains for me to examine its relations 

 to the other forms of this group. The fact that the first row of spots 

 covers the first and second rows anteriorly seems to furnish some evi- 

 dence that the stripe is to be considered on the third and fourth rows. 

 Still, this is, of course, not conclusive, and the lateral stripe must still 

 be considered noncommital, although the fact that it occurs on the 

 second and third rows posteriorly is not an insurmountable objection, 

 as it also has this position in megalops, in which it is anteriorly upon 

 the third and fourth rows. The number of labials is much the same 

 in both marcianus and megalops, as is also the tail length. On the 



