880 On Aquatic Carnivorous Coleoptera or Dytiscidce. 



developed, wings of metasternum short ; hind femora with well developed lamina 

 at postero-external angle. Sexual disparities on legs remarkable, of sculpture 

 none. 



The group consists of two very similar North American species. 



Group 7. 



Hind coxae small, wings of metasternum large, hind tarsi feeble, but hind femora 

 with distinct lamina at postero-external angle ; male front claws short and dentate 

 beneath ; no abdominal file ; prosternal process not, or slightly, compressed, 

 glabrous or feebly punctate, either narrow or moderately broad : cilise at angle of 

 lower surface of hind femur very rudimentarv. 



I have associated these three species together to avoid multiplying the groups, 

 but they are discordant, and have affinities in different directions, and the group 

 so constituted is not a natural one. 



Dytiscus uliginosus is a peculiar species with small coxse, compressed and 

 punctulate prosternal process, and very imperfect metasternal groove ; it approxi- 

 mates to the 12th group. 



Colymbetes semipunctatus has the prosternal process comparatively broad, 

 polished, and little compressed, with a deep and well developed metasternal groove, 

 and approximates to the second group. 



Agabus seneolus has the wings of the metasternum smaller than the above species ; 

 the prosternal process is a good deal compressed, and the species seems to be really 

 more allied to Dytiscus femoralis, than to the proceeding insects, but it has the 

 wings of the metasternum larger. 



Group 8. 



Form narrow and parallel ; males with short anterior claws, dentate beneath, 

 and with a series of strias forming a file (no doubt a stridulating organ) on each 

 side of the third ventral segment : the prosternal process is rather narrow, and 

 very little compressed, nearly glabrous, or feebly punctulate ; the anterior border 

 of the hind coxse is much arched, the wings of the metasternum are moderately 

 large ; the hind tarsi are rather feeble, but the femora have a distinct lamina at 

 the postero-external angle : the ciliae at this spot are very rudimentary. 



This is a natural group of very similar species, distinguished by the peculiar 

 stridulating organ of the males ; this is very highly developed in Agabus stridulator ; 

 the hind femora possess a fine indistinct raised margin on their upper anterior 

 edge ; I think sound can only be produced by this apparatus when the bind body 

 is distended, or made prominent at the spot where the rugae are. 



