172 REPTILES. 



ORDER Y.-OPHIDIA. 



(The Sei'pents.) 



Reptiles, not shielded, with an epidermal covering of 

 imbricated scales, which is shed as a whole and replaced 

 at regular intervals. Mouth very dilatable, the bones of 

 the lower jaw separate from each other, only united 

 by ligaments. Limbs wanting, or represented by small 

 spurs on the sides of the vent; vent a transverse slit. 

 Various anatomical characters distinguish the snakes, 

 but the elongated form and absence of limbs separate 

 them at once from all our other Vertebrates, excepting 

 the Lizard Opheosaurus^ and this is not in any other 

 respect, snake-like. 



FAMILY LXXV. () COLUBRIDJS. 



(TJie Colubrine Snakes.) 



Both jaws fully provided with teeth, which are conical 

 and not grooved; head covered with shields; no poison 

 fangs; no spur -like appendages to vent; belly covered 

 with broad band -like plates (gastrosteges) ; tail conical, 

 tapering; sub -caudal plates (urosteges) arranged in 

 pairs. 



A very large family comprising nearly one hundred 

 genera, and upwards of four hundred species, found 

 in nearly every part of the world, but most abundant in 

 warm regions. They differ from the Elapidce of the 

 Southern U. S. and southward, in the want of erect 

 poison fangs; from the Crotalidce, in having both jaws 

 fully provided with teeth, and the absence of erectile 

 poison fangs; and from the Boidce and their relatives in 

 the want of the spur -like rudimentary posterior limbs. 



The following key is entirely artificial, and in the 

 consideration of the species, I have generally omitted 



