Introduction 



With both snakes and lizards the character of the scales 

 of the upper surfaces, is important. The scales may be smooth 

 or keeled (carinated); in the latter case, weakly or heavily keeled. 

 A keeled scale has a distinct, line-like keel running from its 

 base to the tip. 



Some of the lizards have a very fme, granular scalation 

 above and large, square shields on the abdomen; others have 

 large, keeled scales above and smaller scales on the under-surface. 

 Many have the head plated, like the snakes; others have small 

 scales on the top of the head. Such details of structure are 

 easily understood and largely employed in the descriptions. 



It should be noted that the body scales of a snake are ar- 

 ranged in symmetrical, oblique rows, from one side of the abdo- 

 men to the other; the abdomen is covered with a single row 

 of broad plates. By counting the scales in one of the rows, 

 on the upper surface, we have another important point to be 

 used in identification. 



The pupil of the eye of snakes or lizards, may be round or 

 elliptical: this should be noted. 



Little more can be said by way of explanation. Preced- 

 ing each Part of the work is a classified list showing the arrange- 

 ment of families, genera and the number of species of North 

 American reptiles in each of the genera. Preceding the de- 

 scription of each list of species of the various genera, is a key 

 to those species. Thus the way is paved, step by step, to assist 

 the beginner. 



Before examining the succeeding chapters, it is interesting 

 to get a bird's-eye view of the subject involved. 



The Class Reptilia is represented in North .America by 

 four Orders given below: 



The Chelonia — Turtles and Tortoises. 

 The Crocodilia — Crocodilians. 

 The Lacertilia — Lizards. 

 The Ophidia — Snakes. 



The total number of North American species of these Orders, 

 is 254. Of these 44 are Chelonians, 2 are Crocodilians, 97 are 

 Lizards and 1 1 1 Snakes. 



xiv 



