OUTLINES AND KEYS 161 



(1) Burrowing s?ud'es, with sliort, round bodies, 

 blunt tails, defective ejes, scant teeth, and no neck. 

 They rarely appear on the surface, and are non- 

 poisonous. 



{'2) Groicnd-snakes^ whicli have bodies not out of 

 the usual, with neck nearly always of different size 

 from the head. They are the snakes loe know usu- 

 ally. Most poisonous snakes belong here, but many 

 are harmless. 



(3) Tree-snakes^ which usually live in trees in 

 warm countries and have slim, whiplike tails of great 

 length. The scales under the bod}^ often have keels 

 or ridges, to prevent slipping sidewise. Some of 

 these are very poisonous, as the various forms of 

 Elaps in South America. 



(4) Fresh-icater snakes^ which live mostly in or 

 about the water, coming on land at times. They 

 have the nostrils closed by valves at the upper edge 

 of the tip of the snout. Tails round. Non -poi- 

 sonous. 



(5) Salt-ioater or sea-sna'kes^ which live in the 

 ocean — only one genus coming rarely on land. They 

 can not move well on it. Their tails are flat like an 

 eel's, and the fin is supported with the spines of the 

 back-bone as were those of the old sea-serpents 

 {Python omoi'ph a) already noted. The young are 

 born in the ocean. They are very deadly — feeding 

 on flsli which they pui'sue and poison before swal- 

 lowing. 



While this arrangement is good so far, it is not 

 based on structure or real kinship. In a crude group- 



