46 C0LE0PTERA OP NORTH AMERICA. 



Our two genera may be separated as follows : — 



Prosternum small, sulcate ; metasternal spine long. Hydrophiuts. 



Prosternum acutely carinate ; metasternal spine short. Hydkochakis. 



Both genera are represented on each side of the continent : 

 the latter genus is called Hydrous by many European authors, 

 which name is more properly a synonym of Hydrophilus : the 

 species of Hydrophilus differ in the proportion of the last joint 

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

 shorter than the penultimate ; in the small ones ( Tropisternus 

 Sol.) the joints are equal, or the last is a little longer than the 

 penultimate.* 



The females of this tribe construct a silky cocoon, attached to 

 plants, under the surface of the water. 



Tribe III.— HYDROBIINI. 



Aquatic species, of an oval or hemispherical form ; the elytra 

 have sometimes ten strise (Berosus), or a large number of rows of 

 punctures (Laccobius), but usually only a sutural stria. A foreign 

 genus (Amphiops) is remarkable for having four eyes, like Gyrinus. 



Many of the species of this tribe have the same general ap- 

 pearance as those of the preceding tribe, but are readily distin- 

 guished by the metasternum not being prolonged behind into a 

 sharp spine. They are all of small size. 



Maxillae with both lobes membranous or coriaceous ; antenna? 

 sometimes 7- or 8-jointed, usually 9-jointed ; middle and posterior 

 tarsi scarcely compressed, sometimes slightly ciliate, with hairs ; 

 first joint short, oblique ; second elongated ; meso- and metaster- 

 num not forming a continuous carina, the latter not prolonged 

 into a spine. 



The following genera, all having five ventral segments, are 

 found in our country : — 



Posterior tibiae and tarsi ciliate; antennae 7-jointed (scutellum elongated). 



Bekosus. 

 Posterior tarsi slightly ciliate ; antenna? 8-joiuted ; posterior trochanters 



large. Laccobius. 



Tibia? and tarsi not ciliate ; trochanters moderate ; antennae 9-jointed ; 



* Vide Proceedings of the Academy of Natural Sciences, vol. vii. p. 368, 

 where may be also found a synopsis of the species of this family inhabiting 

 the United States. 



