880 On Aquatic Carnivorous Coleoptera or Dytiscide. 
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 coxe 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: cilize at angle of 
lower surface of hind femur very rudimentary. 
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 coxe, 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 zeneolus 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. 
Grovp 8. 
Form narrow and parallel; males with short anterior claws, dentate beneath, 
and with a series of strize 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 cox 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 ciliz 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 hind body 
is distended, or made prominent at the spot where the ruge are. 
