SERPENTES 623 



THE REPTILES OF 

 WESTERN NORTH AMERICA 



Suborder II. SERPENTES (Snakes) 

 SYNOPSIS OF FAMILIES 



a. Tail cylindrical or conical, not oar-shaped, 

 b. Ventral scales less than twice as broad as dorsals. 



Plates on top of head not larger than those on body; 

 anus bordered in front by a single plate; a small spine 

 at end of tail. 



Leptotyphlopidac. p. 624. 



b'. Ventral plates more than twice as broad as dorsal 



scales. 

 c. No rattle at end of tail; no pit between nostril and 



eye. 



d. A small spur at each side of the anus; tail short 

 and truncate, or top of head with small scales; 

 pupil vertical. 



Boidae. p. 630. 



d'. No spur at side of anus; tail tapering; top of head 



with large plates; pupil round or vertical. 

 e. No enlarged fangs at front of mouth; coloration, 

 if in rings, not red separated from black by 

 white (yellow). 



Colubridae. p. 644. 



e'. A pair of large permanently erect fangs near 

 front of upper jaw; coloration, in rings, red 

 separated from black by white (yellow). 



Elapidas. p. 887. 



c". A horny rattle at end of tail; a pit between nostril 

 and eye; a pair of large erectile fangs; pupil vertical. 



Crotalidas. p. 893. 



