REPTILES 221 



Family 5. Crotalidae. — Rattlesnakes and copperheads; viperine 

 snakes. Poisonous snakes with a thick body, a slender neck and aflat, 

 triangular head; upper jaw without soHd maxillary teeth, but with a 

 pair of long poison fangs which are perforated each with a canal opening 

 at the tip and lie against the roof of the mouth when not in use, but are 

 erected or directed forward when the animal strikes; a deep pit present 

 between the eye and the nostril; pupil vertical; subcaudals mostly 

 undivided; anal plate undivided; the end of the tail in most species com- 

 posed of horny rings (the rattle); scales keeled: 3 genera and about 18 

 species in the United States; about 6 genera in the Neotropic region and 

 4 genera in the old world; viviparous, but few young produced at a 

 birth, at most a dozen or fifteen. 



Key to the United States Genera of Crotalidae 



ai No rattle present i. Agkistrodon. 



32 Rattle present. 



bi Top of head covered with plates (Fig. 126) 2. Sistrurus. 



ho Top of head covered with scales (Fig. 127) 3. Crotalus. 



I. Agkistrodon Beauvois. Head covered with 9 symmetrical 

 plates; no rattle present; scales in 23 or 25 rows; upper labials 8; ventrals 

 130 to 150; anterior subcaudals undivided, posterior ones divided: 

 10 species, 7 in Asia, 2 in the United States. 



Key to the Species of Agkistrodon 



ai Scales in 2;^ rows; loreal plate present A. mokascn. 



a 2 Scales in 25 rows; loreal plate absent 4. pise Ivor us- 



A. mokasen Beauvois {A. contortrix L.). Copperhead; moccasin 

 (Fig. 124). Length 830 mm,; tail 120 mm.; 

 color light brown, with about 15 transverse 

 bands of darker brown which are narrow on 

 top and very broad at the sides; head copper 

 color; belly whitish, with a series of large ^^<^- -^^a.— Agkistrodon mokanse 



•' ■ ^ ° {from Cope). 



dark spots on each side: Massachusetts to 



northern Florida; westward to Illinois and Texas; sometimes abundant 

 in swampy or rocky places, feeding on frogs, rodents, birds and snakes; 

 bite very dangerous. 



Subspecies of A . mokasen 



A. m. mokasen Beauvois, Cross band narrow: eastern States. 

 A. m. laticinctus Gloyd and Conant, Cross bands wider: Texas and 

 Oklahoma, 



