HYDllOPinLIDAE. 71 



Maxilla; with hotli lobes conicous ; antenna) t)-joiiitcd, rarely 

 7-j()iiited. Tarsi not natatorial; lirst joint subconnate with the 

 second, f're(inently indistinct; 2-4 moderate, subeqnal, the second 

 in Helophorus st)nie\vlKit longer than the first. Thorax narrower 

 at the base than the elytra, in Helophorus and Oclithebius 

 marked with five sinnous longitudinal stria?; elytra with ten striae 

 or rows of punctures, except in Jlydra;na, where the rows are 

 more numerous. 



Sepidiihnn Lee. is synonymous with Epimetopus: one species 

 occurs in Texas ; the other genera occur on both sides of the 

 C(jntinent. 



Last joint of maxillary palpi longer than the preceding ; 



Antennae O-jointcd ; all the palpi moderately long. Helophorus. 



Antennae 7-jointed ; labial palpi .short. ' Hydrochus. 



Last joint of maxillary palpi shorter than the preceding, siibulati- ; 



Eyes nearly divided. Epimetopus. 



Eyes entire. Ochthebius. 



Maxillary pali>i exceedingly long. • Hydraena. 



Tribe II.— HYUROPniLlAI. 



Aciuatic species, of an oval or elliptical convex form, olive- 

 black, rarely with the sides of the thorax and elytra yellow, the 

 latter not striate. 



Maxilloe with both lobes coriaceous; antenna; 9-jointed ; mid- 

 dle and posterior tarsi strongly compressed, fringed internally 

 with long liairs ; first joint short, second elongated ; meso- and 

 metasternum forming a continuous keel, which posteriorly is pro- 

 longed into an acute spine; last joint of the anterior tarsi of the 

 male in some species distorted, with very unequal claws; in the 

 same sex the club of the antenna? is sometimes irregular. 



Our two genera may be separated as follows : — 



Prosternum small, sulcate ; metasternal spine long. Hydrophilus. 



Prosternum acutely carinate ; metasternal spine short. Hydrocharis. 



Both genera are re{)resented on each side of the continent: 

 the latter genus is called IIi/d?-ous by many European authors, 

 which name is more properly a synonym of llydro})hilus : the 

 species of Hydrophilus difler in the proportion of the last joint 

 of the maxillary palpi : in the larger species the last joint is 

 shorter than the i)enultimate ; in the smaller ones (Tropisternus 



