64 BULLETIN 61^ UNITED STATES NATIONAL MUSEUM. 



the rivor valleys. The eastern limit of its known range is repre- 

 sented by the Victoria, San Antonio, and Austin records, and is 

 approximately the 98th mericHan, which, as we have seen, marl^s 

 the boumlary between the prairie type of biota of central Texas 

 and th(> forests of southeastern United States. The most northern 

 record is Fort Supply, Oklahoma (see p. 69). The range of this 

 form then ma}^ be defmed as the arid deserts of northern Mexico, 

 southeastern Arizona, southern New Mexico, and southwestern 

 Texas, the arid plains about the lower part of the Rio Grande, and 

 the prairie region of central Texas. 



Variation. — The individuality of marcianus is so pronounced that 

 it stands out in strong relief from the other forms in the region 

 which it occupies, and makes the question of its affinities a very 

 puzzling one. At the same time it is a very homogenous form and 

 apparently varies but little either geographically or individually, as 

 shown by the fact that but one other variety {nigrolaieris, Brown, 

 1889), based on an anomalous specimen, has been made from it, a 

 form since dropped. 



Any discussion of the variations of marcianus must be made with 

 great caution in consequence of the inadequate number of speci- 

 mens available. Although the material in the American, Field, and 

 U. S. National Museums, and the Philadelphia Academy of Natural 

 Sciences have been examined, besides a number of specimens from 

 private collectors, it has been impossible to obtain more than 60 

 individuals of this form. Fortunately these appear to be scattered 

 over most of the range of the species, and this with the apparent 

 lack of marked individual variation makes it possible, even with 

 but a few specimens from the different localities, to examine the 

 geographic variation. In every specimen examined from Tucson, 

 Arizona, to Oklahoma, the scale rows are 21-19-17. 



The supralabials are more variable; at Tucson they are constantly 

 8 in 5 specimens; at San Antonio, 8 and 9; in Cameron County 

 they are 8 in the great majority of cases, occasionally 7, and in one 

 case 9 on one side, with an average of 7.9; in Oklahoma 8. Evi- 

 dently from the material at hand it is impossible to say that there 

 is any geographic variation in this character. As regards the ven- 

 tral plates, the females have 151 to 156, in the specimens labeled 

 "Yuma, Arizona," and the males 157 to 162, with an average (all 

 specimens) of 155.6; at Tucson two males have 160 and three 

 females 156-159, average 158.4. At San Antonio a female has 149 

 and a male 157; w^iile in Cameron County the range in variations 

 of both males and females are lowered, in oidy two cases reaching 

 160 and falling as low as 144, the average being 151. At White 

 Horse Springs, Oklahoma, a male has 157 and a female 155. These 

 figures seem to indicate a slightly larger number of gastrosteges in 



