278 CAPTAIN F. WALL ON 



which is peculiar to one species only, and which may be seen at a glance, has escaped 

 notice. 



The points which I consider essential in classifying the members of the family are : — 



(i) Rostral, — the portion seen above compared with the length of the suture between 

 the nasals varies considerably. In many species of Distira it is decidedly less than half, 

 and in many species of Hydiophis considerably more than half. 



(ii) Prefrontals, — the relationship of the praefrontals with the supralabials is of ex- 

 treme importance. The rule is for them to touch the 2nd supralabials. In one species they 

 touch the 3rd supralabials, viz., in Hydiophis cantoris, and this single point will suffice to 

 distinguish the species from all others. Again, in a few species they touch no supralabials, 

 notably in Hydrophis nigrocinctus, H. alcocki, H. melanocindus , Distira jerdoni, D. 

 viper ina, and D. hendcrsoni. 



(iii) Frontal, — this shield is rather broader than the supraocular shields in all the 

 species, but in D. viperina alone it is from twice to three times as broad. Again this 

 shield touches six shields in every sea snake except one, viz., Platurus colubrinus, where 

 it touches seven. The sutures which it makes with surrounding shields are important. The 

 parietal sutures are almost always the largest, and this is a character almost peculiar to 

 the hydrophiids as a group. The parietal sutures are not nearly twice as large as the prae- 

 frontals in the majority of species, but in two at least they are fully so, viz., Hydrophis 

 nigroienctus and Distira hendersoni. Again the supraocular sutures are the smallest in 

 one species only, viz., D. viperina. 



(iv) Parietals, — these shields touch one postocular as a rule. I only know of one 

 exception, viz , Hydiophis cccrulescens, in which species the parietals fail to touch the 

 postocular. As already noted by Mr. Boulenger and others, these shields are broken up into 

 small scales in EnJiydris cur tics, but they do not qualify this observation by remarking that 

 the feature is peculiar to this species. 



(v) Nasals, — in many species sutures run from the nostril outwards, and when present 

 they almost invariably (except in some abherrant examples of one or two species) Irun to 

 the 2nd supralabial. In one snake, however, Enhydris hardwickii, this suture, which is 

 always present, runs to the 1st supralabial, and on this point alone the identity of the 

 species is almost certain. 



(vi) Loical, — only one sea snake known to me possesses normally a true loreal 

 shield, viz., Distira hendcrsoni. 



(vii) Temporals, — the number of the anterior shields is important, and this feature 

 together with the character and number of the succeeding shields bordering the parietals 

 has been given due prominence by Giinther. 



(viii) Marginals, — sometimes one or more small wedge-shaped scales are intercalated 

 between the infralabials at the labial margin. These little scales, insignificant as they 

 may appear, are of great importance. To begin with they are seen in only one land 

 snake, viz., the Cobra, where one is wedged between the 4th and 5th. Many sea snakes 

 have none, notably//! nigiocinctus, H. gracilis, H. cantoris, D. jerdoni, D. ornata, and 

 Enhydrina valakadyen. In a few a whole row borders the lower lip behind the 2nd 

 infralabial, viz., in the genus Platurus and in Distira cyanocincta. In D. brugmansii there 



