DYTISCIDAE. CI 



Mesostcrnum short, concealed by the prolonged proster- 

 num, the coxai small, their cavities closed externally by the 

 epiniera. 



Metasternum moderate in length, prolonged in front, and 

 widely separating tlie middle coxie, posteriorly slightly pro- 

 longed and acute between the coxa?, the antecoxal piece 

 entire, -the episterna and epimera distinct. 



Posterior coxte contiguous at middle, attaining the in- 

 flexed edge of tlie elytra at sides, furnished with broad 

 plates contiguous internally, which conceal the posterior 

 legs at their basal half, and from three to six ventral seg- 

 ments. 



Abdomen with six segments, the anterior three connate. 



Legs slender, not natatorial; anterior tibiie entire, spurs 

 both terminal, posterior femora clavate at base; tibial spurs 

 slender; tarsi live-jointed, slender; claws slender. 



This family contains a small number of aquatic genera, which 

 had been associated more or less closely with the Dytiscidas by 

 the older authors. More recent systematists have made of them 

 a separate family intermediate between the Carabidoe and Dytis- 

 cidiB. 



The three genera contain species of small size, oval, more or 

 less pointed behind and in front, and very convex; their color is 

 yellowish, more or less spotted with black. The elytra have rows 

 of punctures, varying in number in the genera. The scntellum 

 is not visible. Tliese insects, while subaquatic in habit, swim but 

 feebly, and with little activity. 



The three genera are thus separated: — 



Terminal Joint of the palpi small, svibulate ; 



Thorax quadrate, with lateral impressed line. Brychius. 



Thorax narrowed in front. Haliplus. 



Terminal joint of the palpi conical, longer than the third ; 



Thorax narrowed in front. Cnemidotus. 



Brychius is represented by one species from California, the 

 other two genera are widely diffused, and the species more 

 numerous. 



Fam. Y. -DYTISCIDAE. 



Mentum deeply emarginate, broadly toothed in the mid- 

 dle; lobes somewhat acute; sides rounded, converging in 



