174 MAJOR F. WALL, I.M.S., O.M.Z.S. 



is to be seen in the type-specimen of Hydrophis aspera from Singapore now considered 

 by Mr. Boulenger as D. cyanocincta, an opinion with which I am in accord. This speci- 

 men in this respect, as in all other important ones, is exactly like the large specimens 

 labelled grandis in the British Museum, which I cannot separate from cyanocincta. 



I cannot derive any help in distinguishing either species or genera from this condi- 

 tion, which appears to me one dependent largely upon age, possibly too upon sex. 



Rostral. — This is entire in all the genera except Thalassophis, where it is divided 

 in one species. A partial, median vertical suture is seen sometimes as an aberrant 

 feature in some species, especially in Platurus schistorhynchus. 1 In Emydocephalus 

 ijimcB it may be furnished with a prominent, sharp spine directed forwards (see fig. 4), 

 but this only occurs in certain individuals and has, I believe, no relation to sex. 



The portion of this shield reflected backwards on the snout varies in some species, 

 but the ranges of variation met with in individuals of the same species overlap so 

 considerably that the point is of very limited importance. In Distira cantoris and 

 D. gracilis the visible portion is from two- thirds to greater than the inter-nasal suture, 

 and in two other slender-necked species, viz., obscura and fasciata, but little less. In 

 nearly all other forms it is less than two- thirds, or even distinctly less than half. 



The contact with surrounding shields is quite constant. In the genus Platurus and 

 Thalassophis, owing to the presence of internasals, it touches five or six shields, five in 

 P. schistorhynchus, six in the rest ; but in all the other genera it touches four shields only. 

 The sutures made with contiguous shields are peculiar in Platurus, the rostro-labial 

 being the longest. In Platurus laticaudatus and P. colitbrinus again the height exceeds 

 the breadth of this shield, whereas in all the other species in the subfamily the reverse 

 condition obtains ; but the degree of breadth relative to height is subject to so much 

 variation in individuals of many of the same species that I cannot utilise this feature 

 in attempting to separate different forms. 



In Enhydrina the lower margin of the shield is projected downwards to be 

 received into the gap in the mental region, and this feature is peculiar to this snake only. 



Nasals. — These are present in every species. Their position is of generic impor- 

 tance in Platurus only , owing to the presence in this genus of internasals. Here the nasals 

 are lateral and separated, and the nostrils lateral ; but in all other genera, except per- 

 haps Thalassophis , the species have nasals in contact with one another on the snout behind 

 the rostral, and the nostrils are superior. Where these shields are superior, sutures 

 are frequently seen running from the nostril to adjacent shields. These are very in- 

 constant in all the species, but there is a decided tendency for a suture to run outwards 

 to the supralabials, backwards to the prefrontals, or inwards towards the opposite 

 nasal. Sometimes three such sutures may radiate from the nostril, and in so doing split 

 each nasal into three parts. The suture running outward is the one most constantly 

 seen, and when present it almost invariably runs to the second supralabial. Exceptions 



1 A similar condition is seen in a specimen of D. cesrule.scens in the British Museum presented by Annandale and 

 Robinson from the Malayan Region. 



