182 .". MAJOR F. WALL, I.M.S., C.M.Z.S. 



departures from the range hitherto recorded are to be expected as the series available 

 becomes enriched in numbers, and especially when specimens are derived from a 

 larger geographical area. It will be seen that my figures for both costals and ventrals 

 in many species exceed those given in Mr. Boulenger's catalogue ; at the same time 

 they are well within the range given for certain other species even in Distira 

 spiralis and cyanocincta into which I have tried to justify the absorption of many 

 other forms previously considered distinct. It certainly appears significant that of 44 

 species recognised by Mr. Boulenger as distinct, and included by him in his genera 

 Hydrophis and Distira, no less than 14 are known from the British Museum alone. It 

 appears to me remarkable that none of these 14 are represented in the many continental 

 and other museums, many of which have large collections of sea snakes. I am forced 

 to think that other herpetologists have recognised the inconsistency of the characters 

 used by Mr. Boulenger in classification, and in consequence have been deterred from 

 describing new species on the uncertain basis offered by many of them. 



Key to the Genera. 



A. Ventrals three or more times as broad as the last costal row in whole body-length. 



(a) Rostral touches 6 shields . . . . . . . . Platurus. 



(b) ,, ,, 4 ,, 



{a ) Two or three supralabials, second very large . . • .. Emydocephalus 



( b' ) Six or more supralabials . . . . . . . . Aipysurus. 



B. Ventrals nearly or more than twice the last costal row in midbody. 



(a) Prefrontal touching the eye, no mental furrow. Ventrals less than 200 HydrElaps. 

 ( b ) Prefrontal not touching the eye. Ventrals more than 200. 



(a') A mental furrow .. .. .. .. .. Enhydrina. 



(&') No mental furrow .. .. .. .. .. Distira. 



C. Ventrals not as broad or little broader than last costal row. 



(a) Costals subimbricate. Prefrontal touches no labial. Frontal and 



parietals broken up . . . . . . . . . . Acalyptus. 



(b) Costals juxtaposed. Prefrontal broken up, or if entire not touching 



second labial . . . . . . . . . . Thalassophis. 



(c) Costals juxtaposed. Prefrontal touches second labial. 



(a') Lowest three or four costal rows enlarged. Ventrals less than 250 Enhydris. 

 (b') Lowest costals not enlarged. Ventrals more than 350 .. Hydrus. 



D. Ventrals absent. Replaced by imbricate scales like the costals . . Astrotia. 



