SERPENTS. 117 



specimens, and so dull in the old that they are nearly 

 entirely of one colour. For example, in the present 

 species, which is called the Black -backed Pelamis, the 

 young snake is yellow below and black above, while 

 the old snake is almost entirely black. 



This species has a very wide range, the specimens 

 in the British Museum having been taken off the shores 

 of India, Borneo, and New Zealand ; and there is one 

 specimen which is believed to have been captured near 

 Madagascar. It is common enough in India to have 

 received a vernacular name, and is called by the 

 natives Nalla Whallagee Pam. 



Then there is a genus of Asiatic marine snakes, 

 which are called by the common titles of Shooter-sun 

 and Chittul by the natives, and are known to zoologists 

 by the generic name of Hydrophis. 



About fifteen species of Hydrophis are in the 

 British Museum ; but there is the greatest difficulty in 

 determining a species of Hydrophis, the marks which 

 are generally used for this purpose being exceedingly 

 variable, not only in different species or in different 

 individuals of the same species, but in the same indi- 

 vidual. 



For example, the shield-scales of the various parts 

 of the head are used as means by which the species 

 can be determined. In the Black-backed Pelamis the 

 specific distinction lies in the number and arrange- 

 ment of the scales about the eyes ; but in some 

 specimens the scales on the one side will be quite 

 different from those on the other, so that it is very 

 possible that mere varieties may be counted as species, 

 or species as varieties. In the British Museum there 



