THE SNAKES 331 



connection with a secondary pit close to the eye and the 

 sigiiiiicant presence of a large nerve leading from it to 

 the brain. At any rate, from a popular standpoint the 

 pit at once brands the Crotaline snake and enables us to 

 abbreviate our subsequent descriptions. 



Among the Crotalince we find one absolutely unique 

 group — the Rattlesnakes. The remarkable caudal ap- 

 pendage is an unfailing character. 



The four genera of the Crotalince may be easily sep- 

 arated, as follows: — 



Without a Rattle. 



Top of head with symmetrical plates. Ancistrodon. 



Distribution : Old and New AVorld. 

 Top of head with small scales. Lachesis. 



Distribution: Old and New World. 

 Tail with a Rattle. 



Top of head with symmetrical plates. Sistrurus. 



Distribution: United States and Mexico. 

 Top of head with small scales. Crotaliis. 



Distribution: North and South America. 



While a number of pit vipers are found in the Old 

 World, the majority of them, the greatest variety of 

 forms and the largest species inhabit the New World. 



Ancistrodon includes both New and Old World spe- 

 cies, ten in number. Of the New World species we may 

 take the Water Moccasin or Cotton-JMouth Snake, 

 A. inscivorus, as a good example. It is a semi-aquatic 

 serpent infesting the lagoons and sluggish waterways 

 of the southeastern portion of the United States. The 

 average Moccasin is about four feet long, dull olive with 

 wide, blackish transverse blotches barely showing on the 

 back, but boldly defined on the sides. The body is very 

 stout and heavy with an abruptly-tapering tail and a 

 chunky, ugly head; the scales are roughly keeled. In 

 lagoons and bayous, where food is especially plenty, the 

 Moccasin grows to a length of six feet ; these big sped- 



