162 BULLETIN 61^ UNITED STATES NATIONAL MUSEUM. 



specimens in the U. S. National Museum labeled "Helotes" and ''near 

 San Antonio," Texas, seem to indicate tliat it also occurs in the 

 prairie region of central Texas, but as these localities are near the 

 margin of the high plateau the range of the species can not be ex- 

 tended into the prairie region until notes on its occurrence in this 

 region are at hand. Just how far north it extends is questionable, 

 but the San Ildefonso specimens show that it attains the high plateau 

 region in New Mexico, which might be expected, since it occurs in 

 the mountains in the Proplateau region (Bailey, 1905, p. 48; Kuth- 

 ven, 1907, 588-589). Similarly its northern limit in Texas also 

 remains to be determined. 



Variation. — Naturally in such an invariable form it is difficult to 

 discover geographic differences in any but large series of specimens. 

 Some differences appear in the material examined, however, which 

 seem to be associated with defuiite parts of the range. In the dia- 

 grams (figs. 71 and 72) I have plotted the variations and mean 

 number of dorsal scale rows and supralabials for various localities 

 throughout the range. 



It is readily granted that the number of specimens employed in the 

 tables is inadecjuate to furnish conclusive results in an investigation 

 of the geographic variation in this form, and yet, in view of the nar- 

 row limits of variation, I believe that the tables are not deceptive 

 in indicating a slight decrease in the number of dorsal scale rows 

 and supralabial scutes in southern Mexico and Central America. 

 The individual variation is too great in the case of the infralabials, 

 ventral and subcaudal scutes to insure accurate results when the 

 available data is tabulated, but I believe when more material is 

 available that the evidence of these characters will not vitiate the 

 evidence of the dosal scale rows and supralabial plates that there is a 

 reduction in scutellation in the region mentioned. The tendency 

 toward a reduction in the number of dorsal scale rows in the southern 

 part of the range is shown in the occurrence of the formula 19-17-15 

 and 17-19-17-15 in specimens from this region, which brings the aver- 

 age below 19-17; wliile similarly the decrease in the number of supra- 

 labials in the same general region is shown in the frequent presence of 7, 

 a number which is not shown in any specimens north of the State of 

 Durango. The latter fact justifies me at once in relegating Cope's spe- 

 cies pulchrilatus (1885 b 174) to the synonomy of eques, as this form 

 was based entirely upon specimens of eques with 7 supralabials. Cope 

 (1900, 1062) objected to this disposition of the form by Boulenger 

 with the statement that it "belongs to a different section of the 

 genus." He neglects to mention, however, which ''section" it is to 

 be referred to, and there is no other evidence besides the number of 

 supralabials that I can find to separate it from eques. 



The limits of variation in the ventral and subcaudal scutes and 

 tail length have already been given. The averages for the larger 



