HYDROPHIIN®A. 265. 
hypapophyses very much developed. Hypapophyses not developed 
throughout the vertebral column. 
Body more or less compressed; eye small or very small, with 
round pupil. MRostral shield with two notches in the oral border, 
only the cleft portion of the tongue being protrusible. 
Marine (with the exception of one species of Distira, confined to a 
freshwater lake in Luzon), entering tidal streams. With the ex- 
ception of Platurus, specimens of which have repeatedly been found 
at some distance from water, these snakes are exclusively aquatic ; 
all are viviparous. They are confined to the Indian and Pacific 
Oceans, one species (Hydrus platurus) being widely distributed, but 
do not seem to occur on the East Coast of Africa. The habitat of 
the greater number extends from the Persian Gulf to the Western 
Tropical Pacific. “ 
Synopsis of the Genera. 
I. Maxillary not extending forwards beyond the palatine; ventral 
shields small or absent ; nostrils on the upper surface of the 
snout. 
A. Symphysial shield triangular, not concealed in a mental groove. 
1. Maxillary longer than the lower aspect of the ectopterygoid, 
with 4 to 18 small teeth in addition to the poison-fangs. 
a. No ventral shields. 
Nostril in the nasal shield.......... 204, Hydrus, p. 266. 
Nostril between two nasals and an internasal. 
205. Thalassophis, p. 268, 
Nostril between two nasals and the prefrontal. 
206. Acalyptophis, p. 269. 
6. Ventral shields distinct, at least on the anterior part of 
the body. 
a. No preocular......... . 207. Hydrelaps, p. 270. 
G. Preocular present. 
Small maxillary teeth not grooved; body often very slender 
“GURATIONR ian, 3 5's canes 3 Sse 208. Hydrophis, p. 271. 
All the maxillary teeth grooved...... 209. Distira, p. 285. 
2. Maxillary not longer than the ectopterygoid, with 2 to 5 
small grooved teeth in addition to the poison-fangs. 
210, Enhydris, p. 300. 
B. Symphysial shield narrow, partly concealed in a deep groove 
WO ERR ns ca emer ns ek < 211. Enhydrina, p. 302, 
