INTRODUCTION. 



Synopsis of Families and Genera, and list of Species of 

 North American Serpents. 



Family I. — Crotalidae. Erectible poison fangs, in front. 

 Few teeth in upper jaw. A deep pit between the eye and nostril. 



Family II. — CoiiUBRiDAE. Both jaws fully provided with teeth. 

 No anal appendages. 



A. Loral and anteorbital both present. 



B. Either loral or anteorbital absent. 



Family III. — Boidae. Both jaws with teeth. Rudiments of 

 hinder limbs or spur-like anal appendages. 



Family IV. — Typhlopidae. Teeth only in one jaw, either 

 the upper or lower. Upper jaw strongly projecting. Scales on the 

 belly instead of scutellse, disposed in several series like those on the 

 upper surface. 



Family I.— CROTALIDiE. 



Tail with a rattle. [^1,^!^ T^" scale-like plates. ...... Crotalus 1 



Top of head covered ->ith large plates arranged as in 



^ [ Coluber Crotalophorus 11 



Tail without a rattle, /present Agkistrodon 17 



Loral plate \ absent Toxicophis 19 



