SNAKES 155 



a bite, the front teeth only and not the grooved fangs 

 pierced the flesh, the poison therefore not being inoculated. 

 The members of this group, which are found in almost 

 every part of the tropical and warmer parts of the world, 

 number about 300 ; they are divided into the following 

 three sub-families — 



1. The Homalopsince, which have valvular nostrils, 

 opening upwards, and are entirely aquatic. 



2. The Dipsadomorphincs , in which the nostrils are 

 situated laterally, and in which the dentition is highly 

 developed. 



3. The Elachistodontince, which have the teeth rudi- 

 mentary. 



The snakes of the sub-family Homalopsina are thoroughly 

 aquatic, a few living in the sea as well as in fresh water, 

 feeding exclusively on fish and crustaceans. Their body 

 is of moderate length, cylindrical, or slightly compressed ; 

 the head is thick, and not distinct from the neck ; the tail, 

 which is of moderate length, is sometimes more or less 

 prehensile, and sometimes compressed at its base. The 

 nostrils, situated on the upper surface of the head, are 

 provided with a valve, which, as in the case of the Croco- 

 dilia, enables them to breath by raising only the upper 

 portion of the head out of the water. All these snakes pro- 

 duce their young alive. Some are gentle in disposition, 

 but cannot be recommended for keeping in captivity, 

 as they invariably refuse food under such conditions. 



Hypsirhina enhydris, a very abundant species throughout 

 the greater part of South-Eastern Asia, is remarkable in 

 being very variable as regards form, some specimens being 



