THE WATER SCAVENOEE BEETLES. 249 



Horn. — "Notes on some Hydrobiini of Boreal America," loo. 

 cit., 237-278. 



Born. — "A Revision of the Spliffiridiini Inhabiting Boreal Amer- 

 ica," loc. cit., 279-314. 



Wickham.— "The Hydrophilidffi of Ontario and Quebec," in 

 Can. Ent., XXVII, 1895, 181, 213. 



About 170 species of HydrophilidcE are known from the United 

 i^tates. These are distributed among foiir tribes, all of which are 

 represented in Indiana. 



KEY TO TBIBES OF HYDROPHILID.E. 



o. Thorax narrower than elytra, usually narrowed behind ; form elongate ; 

 sculpture usually rough ; length less than 6 mm. 



Tribe I. Helophoeini, p. 249. 

 aa. Thorax at base as wide as elytra, narrowed In front ; form usually con- 

 vex, oval or elliptical ; sculpture usually weak. 

 h. Middle and hind tarsi with first joint short. 



c. Metasternura prolonged into a distinct spine; tarsi compressed. 



Tribe II. Htdeophilini, p. 254. 

 cc. Metastemum not prolonged ; tarsi not compressed. 



Tribe III. Hydkobiini, p. 257. 

 hi). Middle and hind tarsi with the first joint elongated; length less than 

 3.5 mm. (except in Sphwridium). 



Tribe IV. SPH^KionNi, p. 265. 



Tribe I. HELOPHORINI. 



Small oblong or elongate aquatic species, gray or brown, more or 

 less tinged with bronze in color. They occur in pools, where they 

 cling to aquatic plants and may be readily taken by stirring up the 

 mud and plants at the bottom, when the beetles will rise to the sur- 

 face. They swim but poorly and are unable to div(» rapidly. Of 

 the five genera into which the tribe has been sc^parated, rppresenta- 

 tives of four occiu' in Indiana. 



KF.Y TO INWANA OENEKA OF HEI.OPIIOTilNI. 



II. Elytra with ten strise or rows of i)iinetures; maxillary palpi moderate. 

 h. Last joint of maxillary palpi longer than the next to last. 



c. Antennas nine-jointed. I. Helophokxis. 



cc. Antennae seven-joinfed. II. Hydrochus. 



66. Last joint of maxillary palpi shorter than the next to last. 



III. OCHTHEBIUS. 



(Id. Elytra with more than ten rows of punctures ; maxillary palpi very long. 



IV. Hyde^na. 



