176 MAJOR F. WALL, L.M.S., C.M.Z.S. 
praefrontal is sometimes, too, divided externally so as to produce a pseudo-loreal. I 
have seen thisin Distira ornata and some other species, but it is an obvious abnormality. 
Fronrat,.—This is present in all species, and, with few exceptions, is normally 
entire. In Aipysurus australis and Acalyp-us peroni it is divided into fragments, the 
integral parts of which, however, taken collectively, clearly reveal the conformation 
of the shield as normally met with in other species. 
It is occasionally divided by a partial or complete longitudinal suture, but the 
condition is an abnormal one. I have seen it in examples of Hydrus platurus, Enhy- 
dris curtus, Distira cerulescens, D. cyanocincta, and others (see figs. 34 and 42). The 
length of this shield relative to that of the supraoculars and parietals has a limited 
importance. In Platurus colubrinus it is much longer, and may even be twice as long 
as the supraocular. In most other species the lengths of each are subequal. In Platurus 
schistorhynchus it is longer than the parietals, but in all other species it is usually 
distinctly shorter. Its length compared with the length of the snout varies consider- 
ably in individuals of the same species, and the ranges of variation for the different 
species overlap so considerably that I cannot utilise the point in their separation, 
though Mr. Boulenger attaches much importance to it. 
The breadth of the shield relative to that of the supraoculars, with few notable 
exceptions, is of no use in assisting the isolation of species. Inallthespecies it is about 
as broad as or a little broader than the supraocular, but in Distiva viperinathe breadth 
is remarkable, amounting to more than twice and often thrice that of the supraoculars 
(see figs. 55 and 56) ; andin Platurus colubrinus and P. laticaudatus it is about twice that 
of the supraoculars. Of equally limited importance is the length of this shield relative 
to its breadth, which I find is about equal in Distiva viperina. In other species the 
length is distinctly in excess of the breadth, but the relative proportions are so closely 
alike in all the species that the point offers no further help in isolating them. 
Again the relative lengths of the sutures it makes with contiguous shields is 
practically the same in all the species, being subequal, or the fronto-praefrontals rather 
the shortest, and the fronto-parietals rather the longest. In the genus Distiva, how- 
ever, two species are peculiar. In D. viferina the fronto-supraoculars are the shortest 
and only about half the length of the fronto-parietals. In D. migrocincta the fronto- 
praefrontals are shortest and only about half the length of the fronto-parietals. 
SUPRAOCULARS.—These shields are present and entire in all forms excepting the 
genus Aipysurus. In A. australis and A. levis they are divided. 
PARIETALS.—These are present and normally entire in all species except Aipysurus 
australis, A. levis and Enhydris curtus, but a tendency to division is very frequently seen 
in individuals of many other species, notably Emydocephalus tjime and Thalassophis 
annandalei. I have seen them divided in a specimen of Distiva cerulescens in the Indian 
Museum (No. 13160), and the tendency to division is also seen in figures 34A, 45C, 60A 
and 66A. ‘They are in contact with the postocular in all the species of the subfamily 
except Distira cerulescens normally, and in a few aberrant examples of Hydrus platurus. 
