SNAKES OF CEYLON. 317 



One notices this in trying to measure a specimen. All goes 

 well till the thickened posterior part is reached, when one 

 has to constantly shift the tape to measure round the curve. 

 The curvature in some species is so pronounced that when 

 the dead snake is laid on its side the body almost completes 

 a circle ! This curious conformation serves the purpose 

 of giving the snake prehensile powers, so that it can wreath 

 the body securely round seaweed and other objects, and so 

 anchor itself. It seems to me probable also, that the body 

 is used to hold its victims until the poison injected has had 

 time to work, for the head is so small in some species that 

 it is difficult to imagine the jaws powerful enough in them- 

 selves to hold a struggling victim of anguine form. The tail 

 is highly compressed in all hydrophids, and forms a fin-like 

 appendage of great service in swimming. The eye is small. 

 It is placed laterally, has a round pupil, and, except in the 

 case of Platurus, the iris is coloured dull greenish. The nostril 

 (except in Platurus, where it is lateral) is large, superior, 

 valvular, and situated in the poster o -external quadrant of 

 a large nasal shield. 



Identificaion. — The fin-like tail at once proclaims a sea- 

 snake, and distinguishes it from all terrestrial and fresh 

 water forms. 



Colouration. — The colouration and the adornment is 

 remarkably similar in nearly all the forms. The dorsum is 

 usually a dirty olivaceous or dull bluish, these hues merging 

 to whitish or yellowish of various shades ventrally. The 

 young are usually very conspicuously banded with dark 

 bluish, greenish-black, or black. The bands are well defined, 

 but tend as age advances to lose definition. Further, it 

 frequently happens that the bands become effaced ventrally, 

 and so converted into dorsal bars. The head in the young 

 is either uniform black or black with a horse-shoe mark 

 on the crown. As age advances the black fades, the horse- 

 shoe is resolved into an indefinite mottling, and ultimately 

 the head becomes a pale olivaceous or pale dirty yellowish. 

 The fact that the colouration is so much alike in all the 

 hydrophids denotes some special purpose. It is probable 



