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 Distiva, 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 oe di i .. PLATURUS. 
(Oy ss ” 4 5, 
(a’) ‘wo or three supralabials, second very large ae .. EMYDOCEPHALUS 
(b’) Six or more supralabials oA ais ae .. 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 HyYDRELAPS. 
(b) Prefrontal not touching the eye. Ventrals more than 200. 
(a’) A mental furrow... Ms be Ae .. ENHYDRINA. 
(b’) No mental furrow a ae .. 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 “6 Bf eA a. .. THALASSOPHIS. 
(c) Costals juxtaposed. Prefrontal touches second labial. 
(a’) Lowest three or four costal rows enlarged. Ventrals less than 250 KENHyYDRIS. 
(6’) Lowest costals not enlarged. Ventrals more than 350 .. Hynprus. 
D. Ventrals absent. Replaced by imbricate scales like the costals .. ASTROTIA. 
