136 



BULLETIN 61, UNITED STATES NATIONAL MUSEUM. 



Variation^ — I have been able to examine but forty-four speci- 

 mens of this form, antl as the locaHties of these are scattered over the 

 entire range the series from each locality is small. The material can 

 not, therefore, be expected to yield definite information as to the 

 extent and nature of the variations. Fortunately, however, the 

 variation in most of the characters is slight. The dorsal scale formula 

 is quite constantly 21-19-17 in every locality, the only variation 

 observed being in the occasional occurrence of the formida 19-21-19- 

 17 in specimens from localities representing every part of the range. 

 The supralabials are 8 in every specimen examined, with the excep- 

 tion of one from San Diego County, which has 9 on one side. The 

 infralabials are nearly as constant in number, as the only specimens 

 in which the number departs from 10 are five, one from San Bernardino 

 County, one from San Diego County, and one from Cartago, all of 

 which have 11 on one side; one from Fort Tejon with 12 on one side, 

 and one from the "South Fork of Kern River," which has 9 on one 

 side. The labial formula is thus quite constantly 8/10 over the entire 



>:- - - -5i> 



7x. 



6 



3 



v.^ 



Fig. 57. 



Tejon, Kern Laice, Cartago, Kern River Kern- 



Cal. Cal. Alvord, Lalces, Cal. ville. 



Bishop, Cal. 



Cal. 



-Diagram showing the variation in the number of preoculars in Thamnophis 

 hammondi. 



range, and much larger series are needed if there are any geographic 

 differences to be revealed in either the labial or dorsal formulas. 



As regards the preoculars the case is different. As previously 

 stated, the number may be 1 or 2, and it is interesting to mention 

 that in a number of specimens examined with 2 the two scales are 

 partially fiksed, which seems to indicate further that the number of 

 preoculars is intermediate. In the table that forms fig. 57 is shown 

 the geographic distribution of this trait. This diagram seems to 

 indicate that in the southern part of the range there is a decidedly 

 greater tendency toward two preoculars than to the northward, a 

 fact which, if true, is a significant one. 



As far as can be determined from the material at hand the number 

 of ventral and subcaudal plates and tail length exhibit no geographic 

 differences, the limits being: Subcaudals, 65-81 (females), 71-96 

 (males); ventrals, 155-171 (females), 164-178 (males); tail length, 

 about .21-. 25 (females), .25-. 27 (males). It is hardly necessary to 

 point out that these limits, based as they are on a small amount of 



