132 VENOMS 
on the upper surface of the snout, between the nasal shields. The 
eyes are always very small. 
The number of species at present known is considerable ; they 
are divided into ten genera. We shall confine ourselves here to 
mentioning the principal diagnostic characters of these genera, 
and to describing the most common species. 
Fic. 77.—SKkuLL or Hydrus platurus. 
(After G. A. Boulenger, op. cit.) 
(1) Hydrus. 
(Fig. 77.) 
Maxillaries longer than the ectopterygoids, not extending 
forwards as far as the palatines; poison-fangs grooved, rather 
short, followed, alter an interspace, by 7 or 8 solid, backwardly 
