170 



BULLETIN 61, UNITED STATES NATIONAL MUSEUM. 



represented in these diagrams are typical for every locality examined, 

 as far as can be judged from the material at hand. 



The ventral scutes var}'^ as follows: Females, 150-165; males, 

 153-178. The average for thirteen specimens from California (west 

 of the Sierra Nevadas) is 161, for twenty Montana specimens, 163.7. 

 The subcaudal plates vary as follows: Females, 65-80; males, 73-92; 

 average number for twelve s])ecimens from California, 82 ; for thirteen 

 specimens from Montana, 81.3. The material at hand is not sufficient 

 to throw much light upon the proportionate length of tail. The 

 extremes are .202-.262 (female), .239-. 32 (males). The average for 

 different localities with more than twelve specimens falls between .23 



Percentage of 

 specimens, 



•8 



.6 4 



.48 



.52 



.16 



.00 



8-8 8-7 7-7 



Supralabials. 

 Fig. 74. — Variation in the number of suprala- 

 bials IN 20 SPECIMENS OF TlIAMNOPHIS SIRTA- 

 LIS PARIETALIS FROM MONTANA. 



Percentage of 

 specimens. 



.90 



.80 

 .64 

 .48 

 32 

 .16 



.00 



11-11 10-10 10-9 9-9 



Infralabials. 

 Fig. 75.— Variation in the number of in- 

 fralabials IN 20 specimens of Thamno- 



PHIS SIRTALIS PARIETALIS FROM MONTANA. 



and .25, but to what extent these averages are constant throughout 

 the range is a question which awaits investigation. 



The more striking variations in color in jMrietalis are j^rincipally in 

 the wa}^ of modifications in the arrangement of spots, the intensity of 

 the ground color, and the color of the interspaces on the skin. It 

 should be recalled that the usual coloration is: Ground color, olive 

 or reddish brown; u])per row of s]wts fused on skin; interspaces about 

 one scale wide and red in color; dorsal stripe on the median and 

 halves of adjacent rows. The variations are as follows: 



(1) Ground color above, Idack; interspaces, narrow (from three- 

 fourths to one-half the width of a scale) ; dorsal stripe on the median 



