DYTISCIDAE. 39 



first sub-family. In common with that series, the Dytiscidae have 

 the side pieces of the mesosteruum diagonally divided, with the 

 epimera reaching the coxa?; the side pieces of the metasternum 

 are narrow, without visible epimera. The middle portion of the 

 mesosternum is entirely covered ; on separating the prothorax, it 

 is found to be deeply sulcate for the reception of the prolongation 

 of the prosternum, which thus firmly unites the different parts of 

 the body, so as to give the stability necessary for rapid motion 

 through the water. 



The body is rounded, sometimes elongated, usually elliptical, 

 rarely very convex. The species are more numerous in the northern 

 parts of the country; they are all winged, and the elytra are always 

 marked with three discoidal, irregular rows of punctures ; rarely 

 the elytra are sulcate (Copelatus, females of certain Dytiscus), 

 frequently punctured, sometimes sculptured with transverse lines 

 (certain Colymbetes). 



The genera represented in our country form two sub-families, 

 so distinct that they might with much propriety be considered 

 separate families. 



Sub-Family I.— HALIPLIDAE. 



Antennae 10-jointed; abdomen covered with large plates of the 

 posterior coxse, which are small and transverse; metasternum almost 

 truncate behind, scarcely emarginate in front; legs scarcely nata- 

 torial. 



This series consists of a single group, containing but two genera, 

 Haliplus and Cnemidotus, of small size; the body is very convex, 

 somewhat acute before and behind, yellow shining, spotted with 

 black or gray. The elytra are covered with rows of punctures; in 

 Haliplus there are nine aud a marginal series, in Cnemidotus there 

 are eleven or twelve. The scutellum is not visible. The insects 

 of this sub-family swim but feebly, and with little activity. 



Palpi subulate. Haliplus. 



Palpi filiform. Cnemidotus. 



Sub-Family II.— DYTISCIDAE (genuiui). 



Antenna; 11-jointed; posterior coxa? without plates, very large 

 (except in the European genus Pelobius) ; legs very natatorial 

 (except in the same genus). 



