AMPHIBIA AND REPTILIA OF COLORADO 107 



Family Crotalidae 

 Pit Vipers 

 This family of snakes is distinguished at once by the peculiar pit 

 on each side of the front of the head below the nostril. This structure 

 although well enervated is of unknown function. The Crotalidae have 

 large movable fangs in the front part of the upper jaw. These fangs, 

 which are hollow, are connected with poison sacks and so arranged 

 that the opening of the mouth elevates the fang. These snakes are 

 venomous, the bite of several species often proving fatal in spite of 

 medical attention. Four species are recorded from Colorado. 



Genus CROTALUS Linnaeus 



Crotalus Linnaeus, Syst. Nat., ed. X, p. 214, 1758. 



Anal plate entire; subcaudal plates entire; genials large; scales 

 heavily keeled, excepting the first two or three rows on each side, in 

 23 to 31 rows; labials, 12 or more, subequal; tail terminating in a 

 jointed rattle. 



The rattlesnakes, of which there are sixteen or more species, range 

 from Canada to Brazil. They are of a specialized and distinctive 

 type. All the species of this genus are viviparous. The young when 

 first born have only the button on the end of the tail and the rattles 

 appear after the subsequent sheddings of the skin. More than a single 

 rattle may be produced in a single year so that the general belief that 

 the age of the snake may be determined by the number of its rattles 

 is without foundation. For food the rattlesnakes generally take 

 warm-blooded prey, birds and small mammals. 



Key to the Colorado Species of Crotalus 

 a. Supraocular plate produced and elevated into a distinct "horn" above 

 each eye; size small, length of adults usually less than three feet. 



C. cerastes Hallowell. 

 aa. Supraocular plate not elevated into a "horn" above each eye; size large. 

 b. Tail whitish or yellowish, crossed with three or four distinct, black 

 rings; back with numerous diamond-shaped areas of blackish. 



C. atrox Baird and Girard. 

 bb. Tail without distinct black rings; colored areas on the back rounded. 



C. confluentus Say. 



