168 



BULLETIN 114, UNITED STATES NATIONAL MUSEUM. 

 Table of scale formulo.e of gentilis. 



Formula. 



23-21 

 21-23-21 



23-21-19 



21-23-21-19 



21-19 



19-21-19 



21-19-17 



19-21-19-17 



19-17 



Total 



^lale. 



Female. 





1 



1 





1 



.. 



1 



3 



9 



9 



1 



1 



5 



. . 



1 



1 



1 





20 



15 



Geographic differences on scale rows can not be detected from the 

 scanty material now available. A notable point is the great varia- 

 bility in formulae. Like the southern forms of the group, 17 rows 

 toward the posterior end of the body is much less common than 19, 

 and this number is possessed almost exclusively by males. The com- 

 monest formula is 21-19. 



Variation in other points of scalation may be considered as only 

 normal for the group. Reduction in the temporals below 2 + 3 + 4 

 occurs frequently in the third row and less often in the first two. 

 There is no evidence that the lower labials are becoming reduced 

 to 8. In fact, it may be said that reduction in scutellation from the 

 mean of the group has not proceeded in gentilis quite as far as in 

 syspila and triangulum. 



In spite of the scarcity of specimens certain significant differences 

 that depend upon locality may be noted in the color pattern, chief of 

 which is perhaps the increase in dark pigment westward. Eastern 

 specimens as a rule have more red on the snout, while examples from 

 west of the Rocky Mountains may have the whole head black with 

 only a very little lightening in the loreal region and at the end of the 

 snout. Likewise on the body, the black pigment increases at the 

 expense of the red, and frequently excludes the latter altogether from 

 the dorsal line, thus presenting a striking resemblance to multicincta of 

 the Pacific region. These differences in pigment are, however, only 

 average ; occasional specimens from east of the Rockies are as heavily 

 pigmented as those west. The latter are definitely ringed, while those 

 on the east side of the mountains show a variation toward syspila. 

 Here the black on the belly opposite the dorsal red areas is sometimes 

 split lengthwise in the middle or is continuous across the belly but 

 much narrower. Thus specimens from Nebraska and Kansas may 

 have the red restricted to wide dorsal saddles, but there are usually 

 no lateral alternating spots. 



