A MONOGRAPH OF THE SEA-SNAKES (HYDROPHIINA). 181 
in sea snakes in common with many other creatures. This laxity is to be seen 
especially in the bloated features, puffy lips, and about the chin shields of senile 
specimens which alters the approximation of the shields, obliterates their detail, 
destroys the clearness and definition of the head lines to such a purpose, that 
a dapper juvenile specimen of the same species appears a different creature. Figures 
22 and 25 exemplify this statement. Incase, however, my views with regard to these 
two forms being identical are not shared by others, I may say that I have seen as 
great a difference in general aspect between young and old specimens in such well 
differentiated species as Enhydrina valakadyn. 
With the exception of the characters above made reference to I can find none 
which possess any weight at all in the separation of the species, and, as has been 
already remarked, many of those referred to are subject to some degree of inconstancy 
in certain species, making them at the best of somewhat uncertain value. Many of 
these very characters, however, cannot be dispensed with ; they are essential to the 
separation of the species of Distiva, but in making use of them one has to guard 
against allowing a single or dual aberration to form the basis of a new species as has 
undoubtedly so often been the case. Naturally it is the species that most lack definite 
characters that have suffered most separation and confusion, especially Distiva spiralis 
and cyanocincta. 
It is more than probable that many of my views expressed above may not be 
completely shared by other herpetologists, and I would remark that I believe that 
the only possible way to establish the constancy of the various shields in a given 
species is bya comparison of these in the gravid female with those of her unborn 
progeny. My opportunities for doing so have been limited, but in one species in 
particular I have been fortunate viz., Enhydrina valakadyn. 1 have had many gravid 
females, and examined the scale characters of each attentively with that of their 
contained foetus. The result was instructive, and modified my previous views consider- 
ably. The inconstancy of many shields relied upon by other authors implicitly in 
classification was found to be proximately similar in the few gravid females of other 
species, notably those of the genus Distiva, which fortune has from time to time 
offered me for examination. 
A series of gravid Distiva spiralis and D. cyanocincta would alone, I feelassured, 
clear up the conception of these species as viewed by me in partial opposition to 
those held by other herpetologists. So far as the numbers of the costals and ventrals 
are concerned, I think it is reasonable to expect to find a proximate range of varia- 
tion in individuals of species which are similar in corporeal habit. Now if one takes 
a well differentiated species such as Enhydrina valakadyn, which could not be confused 
with any other, the costals in the neck according to Mr. Boulenger’s showing 
vary within twenty in individuals. A similar range is recorded by him for the body 
scales. ‘The ventrals by the same authority's showing vary by 84. Now in some of 
the genus Distiva, where a large series of specimens is available and these from the 
widest geographical area, a proximate degree of variation is seen in the costals, and 
even an excess in the range of the ventrals amounting to 155 in fasciata. Moderate 
