HYDROPHIINiE. 



179 



Subfamily HYDROPHIIN^. 



Synopsis of the Genera. 



I. Ventral sliields, if at all distinct, very small. 

 A. Nasal shields in contact with each other 

 on the median line of the snout. 



1. Symphysial shield exposed. 



No ventral shields ; scales all juxtaposed .... Hydrus, p. 180. 

 Ventral shields distinct at least in the anterior 



part of the body ; scales imbricate in the 



anterior part of the body Hydrophis, p. 181. 



Ventral shields distinct at least in the anterior 



part of the body ; scales all juxtaposed .... Enhydris, p. 192. 



2. Symphysial shield narrow, partly con- 

 cealed in a deep groove in the chin . . Enhydrina, p. 193. 



B. Nasal shields separated by internasals ; 



scales all juxtaposed Thalassophis, p. 194. 



II. Ventrals large ; scales all imbricate. 



Nostrils on upper surface of snout Aipysurus, p. 195. 



Nostrils lateral Platubus, p. 19G. 



Fig. 65. — Views of right maxillo-palatal arch. 



A. Platurus. B. Enhydris. C. Hydrus. 



m. Maxillary, pi. Palatine, j^t- Pterygoid, tp. Transpalatine or Ectopterygoid. 



The presence or the absence of a groove on the small teeth behind 

 the poison-fangs has been used by nie for defining genera, but it 

 has been shown, by Stejneger and by Wall, that this character 

 must be given up, the groove being found to be present in 

 species believed to be deprived of it, when a sufficiently strong 

 magnifying power is applied to the examination of the teeth. The 



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