SNAKES OF CEYLON. 255 



Habits. — Aquatic. They inhabit lakes, rivers, and coasts. 

 As far as is known all are viviparous. 



Food. — Exclusively fish. 



Poison. — Very feebly poisonous, innocuous to man. 



Lepidosis. — Head covered above with large shields of the 

 Colubrine type. 



Costals : Longer than broad ; rectiform throughout ; keeled 

 or smooth. Ventrals : Narrow, about three times the breadth 

 of the last costal row ; rounded or obtusely keeled laterally. 

 Anal : Divided. Subcaudals : Divided. 



Distribution. — South-east Asia, Papuasia, North Queens- 

 land. 



Ten genera are known, two of which are represented in 

 Ceylon, viz., Cerberus and Gerardia. 



Genus CERBERUS. 



(Greek " kerberus " the famous three-headed dog that guarded 



the entrance to Hades in Grecian mythology. The name 



appears to have been suggested by the forbidding 



aspect of the snake, which has the jaw 



very under hung.) 



General Characters. — Smallish snakes, 2 to 4 feet in length. 

 Head pear-shaped as seen from above, expanding considerably 

 towards the occiput. Snout narrow, in profile showing an 

 unusually prominent lower jaw, little shorter than the upper. 

 This feature to a large extent gives the snake its forbidding 

 expression. Nostrils directed almost as much upwards as 

 laterally, narrow slits convex forwards. They approach the 

 condition seen in the seasnakes. Eye rather small, directed 

 as much upwards as laterally, with the eyebrow remarkably 

 prominent. Iris minutely speckled with gold, revealing a 

 vertically elliptical pupil. Neck fairly evident. Body stout 

 and rough from the strong keels on the costal scales. It is 

 dull dorsally, glossy on the belly, including the last three 

 costal rows. Belly rounded. Tail short, rather compressed 

 at the base, and rapidly tapering to a subacute point. It is 

 about one -fifth the total length of the snake. 



