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



praefrontal is sometimes, too, divided externally so as to produce a pseudo-loreal. I 

 have seen this in Distira omata and some other species, but it is an obvious abnormality. 



Frontal. — 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 ccerulescens, 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. In all the species it is about 

 as broad as or a little broader than the supraocular, but in Distira viperina the breadth 

 is remarkable, amounting to more than twice and often thrice that of the supraoculars 

 (see figs. 55 and 56) ; and in 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 Distira 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 Distira, how- 

 ever, two species are peculiar. In D. viperina the fronto-supraoculars are the shortest 

 and only about half the length of the fronto-parietals. In D. nigrocincta 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. Icevis they are divided. 



Parietals. — These are present and normally entire in all species except Aipysurus 

 australis, A. Icevis and E 'nhydr is curtus , but a tendency to division is very frequently seen 

 in individuals of many other species, notably Emydocephalus ijimcB and Thalassophis 

 annandalei . I have seen them divided in a specimen of Distira ccerulescens 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 ccerulescens normally, and in a few aberrant examples of Hydrus platurus. 



