16. CROTALIDM 



and tail, while the rest of the body is rested on the inter- 

 vening loop, supporting the rest of the body, the weight 

 then seems to be shifted to the head and tail and the rest 

 of the body advanced, the whole progression being a series 

 of graceful continuous movements. This seems to be the 

 mode of progression." 



Mr. Slevin found a pair mating under a bush on the 

 desert west of Barstow, San Bernardino County, California, 

 at about five o'clock in the afternoon, during the last week 

 of April, 1913. 



219. Crotalus willardi Meek 



Willard's Rattlesnake 



Plates 105 and 117 



Crotalus willardi. Meek, Field Columb. Mus., Zool. Ser., Vol. 7, No. 1, 

 1906, p. 18, pi. Ill (type locality, Tombstone, Arizona); 

 MocQUARD, Miss. Sci. au Mexique, Pt. Ill, Rept., 1909, p. 972; 

 Hartman, Proc. U. S. Nat. Mus., Vol. 39, 1911, p. 569, fig. 1-4; 

 Van Denburgh & Slevin, Proc. Cal. Acad. Sci., Ser. 4, Vol. 3, 

 1913, p. 394; Stejneger & Barbour, Check List. N. Amer. Amph. 

 Rept., 1917, p. Ill; Swarth, Copeia, 1921, No. 100, p. 83 (type 

 locality stated to be Hamburg, Ramsey Canyon, Huachuca, 

 Mts., Arizona). 



Descriftion. — Moderately large. Head long, with 

 flattened top and rather narrow, elevated snout. Rostral 

 higher than wide, in contact with anterior nasal. Two nasals. 

 Upper preocular large, not divided vertically. Internasals 

 rather small, as long as wide, turned up anteriorly into the 

 prominent canthus rostralis. Supraocular large but not 

 raised into a horn-like process} separated from its fellow 

 by about seven to nine irregular rows of scales. Supralabials 

 13 to 15, separated from eye by about two rows of scales. 

 Infralabials 13 to 15, first pair in contact on median line in 

 front of a single pair of genials. Scales on body in 25 or 



