i8o REPTILES AND BATRACHIANS 



Atheris^ of Tropical Africa, is a genus composed of 

 four or five small arboreal species ; the very distinct head 

 is heart-shaped and covered with small scales. The 

 body and the prehensile tail, the scales upon which are 

 keeled, are compressed. The fangs are moderately- 

 developed. Tree-frogs form the only food of these 

 vipers. 



A. dorechis, of West Africa, which at the most grows 

 to two feet in length, is bright green in colour, being 

 perfectly inconspicuous when coiled among the foliage 

 of the branches upon which it lives. 



Atractaspis, of Tropical and South Africa, represented 

 by about fifteen small snakes, none of which attain a length 

 of more than thirty inches, are all highly poisonous, the 

 poison fangs being enormously developed, larger in pro- 

 portion than in any other snake. I was myself on one 

 occasion bitten on the finger by a fifteen-inch-long 

 specimen of A. irregularis, and in spite of the fact that 

 one fang only pierced the flesh, and that every endeavour 

 was made to prevent the absorption of the poison, the 

 effects were most pronounced, being felt for several days. 



The Pit-Vipers, sub-family Crotalince, are inhabitants 

 of Southern Asia and Southern and Central America, and 

 are represented by four genera, which may be distinguished 

 as follows — 



A. No rattle. 



1. Upper surface of head covered with nine symmetri- 

 cal shields, Ancistrodon. 



2. Upper surface of head covered with scales or small 

 shields, Lachesis. 



