THE W ATE IT SCAVENGER BEETLES. 

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249 



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

 tit, 237-278. 



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

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



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

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



About 170 species of Hydrophilid* are known from the United 

 States. These are distributed among four tribes, all of which are 

 represented in Indiana. 



KEY TO TRIBES OF HYDROPHILID^E. 



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

 sculpture usually rough ; length less than 6 mm. 



Tribe I. Helophorini, p. 249. 

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

 vex, oval or elliptical ; sculpture usually weak. 

 J). Middle and hind tarsi with first joint short. 



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



Tribe II. Hydrophilini, p. 254. 

 cc. Metasternum not prolonged ; tarsi not compressed. 



Tribe III. Hydrobiini, p. 257. 

 1)1). Middle and hind tarsi with the first joint elongated; length less than 

 3.5 mm. (except in Sphwriclium) . 



Tribe TV. Sph.ertdiini, 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 dive rapidly. Of 

 the five genera into which the tribe has been separated, representa- 

 tives of four occur in Indiana, 



KEY TO INDIANA GENERA OF HELOPHORINI. 



a. Elytra with ten striae or rows of punctures; maxillary palpi moderate. 

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



c. Antennas nine- jointed. I. Helophori s. 



cc. Antennae seven-jointed. II. Hydrochus. 



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



III. Ochthebius. 



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



IV. Hydr.ena. 



