12 COLEOPTEKA OF iNORTH AMERICA. 



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

 penultimate. 



The females of this tribe construet 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 

 liavc sometimes ten striae (Berosus), or a large number of rows 

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

 foreign genus (Amphiops) is remarkable for having four eyes, 

 like Gryrinus. 



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. 



Maxilh^ with both lobes membranous or coriaceous; antenna? 

 .sometimes T- or 8-jointed-, usually 0-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 occur in our fauna: — 



A. — Labrum visible ; epistoma not dilated. 



Last ventral segment entire. 2. 



Last ventral segment emarginate. Berosus. 



2. "Ventral segments not covered. 3. 



First and second ventral segments concealed by plates. 



Chaetarthria. 



:3. Ventral segments five ; tip of sixth sometimes visible. 4. 



Ventral segments more tlian six. Limnebius. 



4. Antennte 0-jointed. ^>- 

 Antennae S-jointed. Laccobius. 



5. Last joint of maxillary palpi shorter than third. Philhydrus. 

 Last joint of maxillary palpi longer than third. Hydrobius. 



B. — Labrnm concealed. by the dilated epistoma. Helopeltis. 



Limnocharis Horn does not differ from Limnebius, which so 

 far has occurred only in California. Sperchopsis Lee. must be 

 united with Hydrobius. Helopeltis larvalis Horn is found in 

 Florida, Louisiana, Cuba, and Mexico. The other genera are 

 widely distributed. 



