180 MAJOR F. WALL, I.M.S., C.M.Z.S. 



species, so that this character is one not to be relied on. Its value and place is on a 

 par with the contact of the praefrontal and supralabials, the condition of the anterior 

 temporals and the arrangement of the marginals, and in no case should new species 

 be based upon any of these characters singly, or even when combined, on the existence 

 of a solitary example, unless there are other good grounds for doing so. 



Colour and Markings. — These vary so in examples from birth to senility, and 

 in many individuals of similar growth, in such well differentiated forms as, for instance, 

 Enhydrina valakadyn and Hydrus platurus, about which there can be no confusion, 

 that I cannot attach the slightest importance to them in classification. So far as the 

 genus Distira is concerned, the species of which present the greatest difficulties in 

 identification, it may be said, as a general rule, that they are marked with annuli in 

 the young. These are usually well defined, complete and conspicuous, but tend to 

 become less defined, partially or entirely obscured, or completely obliterated with 

 age. It is noteworthy, too, that in many species where the head is completely black 

 in the juvenile state, it loses its depth of hue with age, very frequently becomes 

 mottled with lighter hues which show a great tendency to the formation of a horse- 

 shoe, or crown-shaped mark, and this in turn may disappear as the whole head 

 acquires a yellowish or light colour. These changes are very remarkable. 



Bodily Configuration. — This in certain forms is very distinctive, but does 

 not influence generic separation owing chiefly to the fact that the genus Distira, as 

 at present understood, contains species exhibiting extremes in the relative proportions 

 of their bodies, between which every degree of relative variation may be found ; thus 

 we see the extremely slender-necked forms of cantoris, gracilis, etc., associated with those 

 of remarkably even girth throughout such as jerdoni and spiralis. I cannot but think 

 that anatomical conditions will be revealed, which will enable the genus, as herein 

 represented, to be split up into three or four genera at least. 



In certain genera the bodies are cylindroid or feebly compressed throughout as 

 Platurus, Emydocephalus and Aipysurus. In the others the posterior part of the body 

 is moderately or extremely compressed.- In certain Distira the anterior part of the 

 body is cylindrical, the posterior very distinctly compressed, especially so in cantoris 

 gracilis, fasciata, obscura and neglecta. I find that the relative girths of the neck 

 and body vary considerably from birth to adult life, in the sexes, and in the female 

 from conception to parturition. In an example of Distira obscura, I have found the 

 forebody considerably more than one-fourth the greatest body depth, and in another 

 very distinctly less than one-fifth, and a very proximate range of variation is seen 

 in other species. In many cases, however, the range given by me is likely to be 

 considerably increased by measurements taken from heavily gravid females. 



The difference in individuals in obscura is considerable, so much so that it is 

 evident that in closely allied species corporeal habit cannot be relied upon to assist 

 the isolation of species. Such terms as " small," " moderate" and (( large" used by 

 many herpetologists in application to calibre are, I need hardly say, far too indefinite. 

 A further remark is necessary regarding the laxity that the tissues acquire in old age 



