CLASS REPTILIA 569 



banded rattlesnake, Crotalus horridus, of the eastern United 

 States; the horned rattlesnake, Crotalus cerastes, inhabiting the 

 deserts of the southwestern United States; and the massasauga, 

 Sistrurus catenatus, which is a rather common species in the 

 central United States. 



4. The Poisonous Snakes of North America 



As the preceding discussion shows, there are only twenty-two 

 species of poisonous snakes in the United States; namely, the 

 harlequin snake, the Sonoran coral-snake, the copperhead, the 

 water-moccasin, seven unimportant opisthoglyphs (p. 563), and 

 fifteen species of rattlesnakes. It is important for any one who 

 spends much time in the country to be able to distinguish be- 

 tween these poisonous snakes and the non-poisonous species. 

 This can easily be done by means of the following key, which was 

 prepared by Professor Alexander G. Ruthven. 



Key to the Venomous and Non-venomous Snakes of the United 



States 



A. Pupil of eye vertical. 



B. A pit between the eye and nostril. — Pit- vipers (venomous) 

 C. Tail terminating in a rattle . . . Rattlesnakes. 

 CC. Tail not terminating in a rattle. — Moccasin and 

 copperhead. 

 BB. No pit between eye and nostril. — Non-venomous or 

 opisthoglyph and not dangerous to man. 

 AA. Pupil of eye round. 



B. Body ringed with red, black, and yellow, the black rings 

 bordered by the yellow ones. — Coral-snakes (venom- 

 ous). 

 BB. Body not ringed with red, black, and yellow, or if so the 

 yellow rings bordered by the black ones. — Non- 

 venomous or opisthoglyph and not dangerous to 

 man. 



