Introduction 



the turtles, are on a straight line (not following the curve of 

 the shell) and were made with calipers in the fashion shown, 

 in miniature, in the illustration. In procuring the width and 

 length of the head; the width of a lizard's body or the greatest 

 diameter of a snake's body, the calipers were necessarily em- 

 ployed. The length of a serpent's head is from the tip of the 

 snout to the back of the bulge, behind the mouth; by running 

 the finger nail along the neck, near the base of the head, the 

 junction of the jaw-bones may be felt; this is the end of the 

 head. (See illustration). The width of the head, is always 

 the widest part. 



"Si^f." -In the descriptive matter will be found the desig- 

 nations, "very small," "small," "moderate" and "large." At 

 the beginning, these sizes should be understood. 



Any of our fresh-water turtles having a shell 10 to 12 inches 

 long, are designated as large species; a small species has a shell 

 from 2 to 4 inches long. 



Lizards under 5 inches in length are small; those between 

 5 and 10 inches long are of moderate size; over 10 inches, they 

 are of large size for North American lizards. 



A snake under 14 inches long is small; over 14 inches 

 and up to 3^ feet might it be described as of moderate size; 

 serpents over 3^ feet long are large among the species em- 

 braced in this work. 



References to structure. In a few of the descriptions, con- 

 cise reference has been made to certain parts of the structure; 

 the resulting terms would be confusing without explanation 

 and figures. 



Turtles. The upper shell is known as the Carapace ; 

 the lower one as the Plastron. For the sake of con- 

 venience, these terms have been frequently used. 



Lizards. As some of the species are more readily 

 separated in the keys by using the arrangement of 

 the head shields as distinguishing features, the student 

 should have a general idea of the situation of the 

 more important head-plates in case there be reference 

 to such. (See illustration.) 



Snakes. The serpents, being scaled reptiles, fall 

 under much the same form of description as the lizards, 

 and a general idea of the head-plates should be acquired. 

 (See illustration.) 



xiii 



