VARIATIONS OF GARTER-SNAKES. 65 



Arizona and a decrease in the Rio Grande Plain, but, while the 

 average for Cameron County probably approximate!}^ indicates tiie 

 actual conditions, the other averages are basetl on far too small a 

 number of specimens to be reliable. The most striking fact shown 

 by these figures is the uniformity in the number of ventral plates 

 throughout the range of the group, for although enough records 

 are not at hand to reveal any slight trends of variation if they are 

 present, enough have been secured to indicate beyond question 

 that such variations, if they actually exist, must be small, as the 

 averages from the different localities differ less than the amount of 

 individual variation in any set of records. The evidence of the sub- 

 caudal plates is especially unsatisfactory, for it is evident that not 

 nearly enough records have been obtained to determine even 

 approximately the range of sexual variation. The specimens 

 labeled "Yuma" vary from 62 to 71, average 66.6. At Tucson 

 the average is 68.6; in Cameron County the average is 68.6, while 

 at White Horse Springs a male has 71. Here again w^e find that the 

 averages when males and females are combined falls between 66 

 and 69, a difference of but 4 scutes and one that could easily be 

 due to the predominance of either sex in the averages. 



As in the case of the subcaudals, it is impossible from the mate- 

 rial to determine the limits of sexual variation in the tail length, 

 yet an examination of the measurements indicates that the males, 

 as a rule, vary from .22 to .26, the general length being between 

 .23 and .24. The females seldom vary more than two points about 

 .21, the range being from .19 to .22. 



It is not to be inferred from the above discussion that there is no 

 geographic variation in the form, for it is possible that when a large 

 enough number of specimens have been examined to establish the 

 limits of sexual variation it will be found that there is some varia- 

 tion in different parts of the range. But nevertheless the evidence 

 now available indicates that if such a variation is present it is small, 

 for even this small amount of material, subject as it is to irregular- 

 ities caused by individual and sexual variation, demonstrates unques- 

 tionably a close uniformity in scutellation and tail length throughout 

 the entire range. 



In color tliis uniformity is even more strongly enforced, and can be 

 no more plainly expressed than by the statement that, owing to the 

 constancy of coloration throughout the extent of its range, no varia- 

 tions have been considered of specific or subspecific value. The 

 ground color is usually light brownish yellow above, with three rows 

 of alternating black spots; the first row on the first, second, and occa- 

 sionally part of the third rows of scales, the other two rows alternating 

 between the lateral and dorsal stripe, on the skin and all but the keels 



