136 SNAKES OF CEYLON. 



without canthus, and the neck fairly evident. The eye is 

 moderate, with a round pupil. The nostril is small, slit-like, 

 and placed rather high, approximating to the condition seen 

 in the true fresh-water snakes (Homalopsinse). The body is 

 fairly robust, cylindrical, and rough from the keeled scales. 

 It attenuates somewhat anteriorly and posteriorly. The 

 belly is rounded. The tail is longish, being about one-fourth 

 to one -third the total length. 



Identification. — The costals in 19 rows anteriorly to behind 

 midbody, 17 behind, and the single internasal shield will 

 distinguish this from aU other Ceylon snakes. It bears a close 

 superficial likeness to Gerard's water snake {Gerardia prevosti- 

 ana). 



Colouration. — (a) Variety typica : Dorsally this snake is a 

 uniform deep ohve-green in life, fading in spirit to olive- 

 brown. The under parts are uniform yellow of varying 

 intensity in different specimens, and this is sometimes suffused 

 with a pinkish or lilac tinge in the flanks. The two colours are 

 "abruptly demarcated on the penultimate row of costals. The 

 head is olive-green above, merging to yellow, or pinkish on the 

 lips. Gunther says the young have a blackish streak from the 

 eye continued on to the forepart of the body. 



In Southern India the specimens exhibit a narrow reddish 

 line along the confines of the 5th and 6th rows above the 

 ventrals, where the scale rows are 19, and the 4th and 5th where 

 17. This line ceases at the vent, and is more conspicuous in 

 males than females. 



(6) Variety nndersoni: In this the internasal shields are 

 two in number, and the 1st and 2nd supralabial shields touch 

 the nasal. It is pecuhar to Yunnan. I have examined three 

 specimens in the Indian Museum, which conform to the 

 characters and colouration of variety typica, except in the 

 particulars specified above. 



Habits. — (a) Haunts : The olivaceous keelback exhibits a 

 strong taste for an aquatic environment, and the position and 

 character of its nostrils conforming to the type seen in the 

 true fresh-water snakes [Homalopsinse) in itself proclaims the 

 snake a water snake by habit. In Fyzabad I got no specimen 



