A MONOGRAPH OF THE SEA-SNAKES (HYDBOPHIINM). Ill 



Pr.£oculars. — 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 Distira individuals occur with 

 two where one is the rule, as in viperina, 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 prseocular and prefrontal in one 

 example of D. jerdoni and two examples of D. obscura. 



Postocuxars — 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 Distira, one sees man}'- individuals showing departures from the normal 

 number. 



SupralabiaIvS. — These are of generic importance in one notable instance, 

 viz. Emydocephalns. 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 

 Distira jerdoni 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. (seefig. 19B). In a few species such 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 A strotia 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. nigrocincta including the type, and 

 in one example of D. ccerulescens (No. 13158 in the 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. For a good example take Distira 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 29B, 

 8 with the third and fifth touching the eye. It appears to me obvious that in all three 

 profile views the third , fourth and fifth touch the eye. In recording these shields in my 



