16. CROTALIDJE 



Description. — Size large. Head broad, flat-topped. 

 Rostral about as broad as high, in contact with anterior nasal. 

 Two nasals. Two preoculars. Three postoculars. Inter- 

 nasal and prefrontal region covered with large plates. Supra- 

 ocular large but not raised into a horn-like process 5 separated 

 from its fellow by from two to seven irregular scales. Four- 

 teen to 18 superior and 15 to 20 inferior labials, first pair 

 of latter in contact on median line in front of single pair of 

 genials. Three to five rows of scales between supralabials 

 and eye. Scales in 25 to 29 rows, keeled except in from two 

 to four rows on each side. Gastrosteges varying from 1 80 

 to 194. Anal not divided. Urosteges varying from 20 to 

 27, a few of the first and last sometimes divided. 



The ground color above is yellow, or yellowish, grayish 

 or brownish olive, marked along the back with a series of 

 dark chocolate or olive brown blotches. These blotches 

 often are irregular in outline and usually contain, on each 

 side, a few scales of the light ground color. In some speci- 

 mens the blotches are separated from each other or bordered 

 by pale yellow scales. A peculiarity of the coloration is 

 that each individual scale usually is of a uniform tint, but 

 occasionally scales are particolored as in most other species. 

 Smaller blotches may or may not be present on the sides be- 

 low or between the dorsal rhombs. Posteriorly the general 

 color becomes browner and the dark markings tend to be- 

 come cross-bars which may show but little contrast with the 

 darkened ground color. The rhombs on the neck often are 

 confluent and many form longitudinal lines. The upper 

 surface and sides of the head are of the same light ground 

 color as the body. The internasal, prefrontal and supraocular 

 regions are blackish brown. A dark brown band runs bac k and 

 down from the eye to the scale above the last supralabial, 

 often becoming indefinite or obsolete posteriorly. There 

 usually is a trace of a similar dark band running down and 



