198 



VERTEBRATE ANIMALS OF THE UNITED STATES 



On the Identification of Snakes. — The length in milUmeters of an 

 average adult specimen from the tip of the snout to the tip of the tail 



Fig. 113. — A portion of the skin of La^npropellis getulus, showing 23 rows of scales {from 



Blanchard) . 



and also the length of the tail alone, are first given, followed by a 

 description of its coloration. Those scales which 

 lack the keel are said to be smooth, and these are 

 jy^ usually much more glistening than keeled scales, 

 which are dull in appearance. In some snakes 

 '"2 only the dorsal scales are keeled, while those of 

 the sides are smooth. The number of rows of scales 

 (Fig. 113) is always important in the description; 

 the number of ventrals is also often important; also 

 the number of subcaudals, and whether a single 

 or a double row is present. Whether the anal 

 plate is single or divided is a very important 

 Fig ii4.-Apor- character (Fig. 114). 



tion of the ventral \ o -r/ 



surface of Abastor In most spccics both dorsal and ventral sur- 



eryihrogr animus: i, r r ^i i i i -.i . • ^ 



ventrals; 2, anal plate faccs of the head are covercd with symmetrical 

 (which is here di- plates, wMch are often important in descriptions 



vided); 3, anus; 4, , 



subcaudals {from (Fig. 1 1 5)' 



^^^^' About 2,400 species of snakes are known, of 



which 126 species occur in the United States, grouped in 5 families. 



Key to the Families of Serpentes 



ai No ventrals present, the belly covered with scales; eyes 



covered with scales i. Leptotyphlopidce. 



a2 Ventrals present; eyes not covered with scales. 



bi No elongate poison fangs in front part of mouth. 



