MARINE SNAKES. 



45 



answers to the aim of modern classification, viz., that it shall 

 correctly express their blood-relationship. 



A glance at Platunis — and, better still, a comparison of its palato- 

 maxillary arch with the same in the other Opisthoglypha — shows it 

 to agree so perfectly with some of the terrestrial Elapines, that we 

 cannot resist the conclusion that it should be regarded as one of the 

 latter, which has become adapted to marine life, in the same way as 

 some of the Aglypha and Opisthoglypha have become modified into 

 such forms as Chersydrus and Hipistes. For it is a fact frequently 

 overlooked, though ascertained by Cantor (4), Stoliczka (16), Theobald 

 (17), and other naturalists in India, that these harmless snakes are as 

 much marine as the Hydrophids, to which they bear so striking a 

 superficial resemblance as to be almost undistinguishable from them 

 when seen wriggling in the fishing nets, or floating or gracefully 

 swimming on the surface of the water. But their tail, although com- 

 pressed, does not assume the oar-shape characteristic of the Hydro- 

 phids, nor are the neural and haemal processes so strongly developed 

 as in the latter. An examination of the scaling of the head also 



Fig. I. — Views of right palato-maxillary arch. A. Platunts; B. Enhydris; C. Hyditis. 

 m. Maxillary ; pi. Palatine ; pt. Pterygoid ; tp. Transpalatine. (From the " Fauna of 

 British India.") 



reveals important differences which show these snakes not to have 

 been derived from the same stock as yielded the Hydrophids, 

 and, therefore, that the resemblance between the two types is 

 merely due to convergence, the result of adaptation to a similar 

 mode of life. 



Then, again, the true Hydrophids, and particularly the genera 

 Hydnis, Hydvophis, Distira, although allied to the terrestrial Elapidae, 

 are, with regard to the structure of the palato-maxillary bones, so 

 much less specialised that it must be assumed that they arose 

 from some no longer existing colubrine type, of which both the 

 terrestrial and marine forms are the descendants. In this instance, 

 therefore, as in so many others^ what appears to form a natural group 

 would be merely an association of converging forms. 



