180 MAJOR F. WALL, 1.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 prefrontal 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 Distiva 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 greattendency 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. 
BopILy CONFIGURATION.—This in certain forms is very distinctive, but does 
not influence generic separation owing chiefly to the fact that the genus Distiva, 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 Dzstiva 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 Drstiva 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 
