A MONOGRAPH OF THE SEA-SNAKES (HYDROPHIIN2),. 177 
PRAJOCULARS.—The absence of these shields is of generic importance in one 
instance, viz., Hydrelaps darwiniensis (see fig. 8); in all other forms they are present, 
but they do not assist the separation of either genera or species. In most of the 
species they are single, but I find in some species of Distiva individuals occur with 
two where one is the rule, as in wiperina, and similarly where two is the rule they are 
replaced sometimes by a single shield. In the latter case a notable example 
is nigrocincta. I have seen a confluence of the preocular and prefrontal in one 
example of D. jerdoni and two examples of D. obscura. 
PosTocuLARS.—These are present in all the species, but are of no importance in 
classification. As will be seen under my remarks dealing with supralabials, authors 
are not agreed what to regard as postoculars, many applying this term to the upper 
part of a divided supralabial (usually the fifth) ; even when the term is restricted, as I 
propose, these shields are of no consequence, for in many of the species, specially of 
the genus Distiva, one sees many individuals showing departures from the normal 
number. 
SUPRALABIALS.—These are of generic importance in one notable instance, 
viz. Emydocephalus. In this genus the second shield is a remarkably long one, bor- 
dering the major length of the upper lip and also touching the eye (see fig. 4B). 
In all the other genera they number five or more, and the third is the first 
of the series to touch the eye; but the inconstancy in the number, disposi- 
tion, and integrity of these shields in individuals of many species is such that 
a very little, if any, reliance can be placed on them in differentiating species. In 
Distiva jerdom there are six, the last of the series being confluent with a large anterior 
temporal shield (see fig. 58), but a similar confluence of the ultimate or penultimate 
supralabial with the anterior temporal is seen in individuals in D. spiralis, D. fasciata, 
D. obscura, etc. (see fig. 19B). In a few speciessuch as D. gracilis, D. cantoris, D. fasciata, 
these shields are very constantly six, but in all the other species of Distira, in Hydrus, 
Enhydrina, Enhydris and Astrotia they vary very much in individuals, and especially 
the posterior shields in the series which are very prone to subdivision. I have seen the 
first subdivided in more than one example of D. migrocincta including the type, and 
in one example of D. cerulescens (No. 13158 inthe Indian Museum). It is divided, too, 
in Jan’s specimen of frontalis (see fig. 34). Thesecond is more frequently so distinguished 
as an abnormal condition, and the succeeding shields in the series become more and 
more prone to division. Fora good example take Distiva cyanocincta. In figure 28 
from a typical specimen the third, fifth and sixth are divided. I do not think any one 
could reasonably doubt that this is the correct way of viewing these shields. In figure 
29 taken from Jan, and acknowledged by Mr. Boulenger among others to represent the 
same species, the same three shields are seen entire on the right side, whilst the fourth 
and sixth are divided on the left side of the same specimen. I think it a mistake to 
record these shields in figure 28 as 8, with the fourth touching the eye, and in figure 20B, 
8 with the third and fifth touching the eye. It appearsto me obvious that in all three 
profile views the third, fourth and fifth touch theeye. In recording these shields in my 
