878 On Aquatic Carnivorous Coleoptera or Dytiscide. 
. Group l. 
Outline of thorax discontinuous with elytra; prosternum but little thickened in 
the middle in front ; swimming legs elongate and slender, the femora feeble, with 
rounded postero-external angle. Mesosternal cavity ill developed. 
The insects associated by the above characters may be looked on as little deve- 
loped forms, as the characters used in defining them indicate. They show no close 
relationship inter se: thus Agabus cordatus has the middle coxze very approximate, 
while in Agabus caraboides they are much more separated ; A. cephalotes is in this 
character intermediate between the two. Agabus abnormicollis seems to approximate 
to Dytiscus biguttatus (No. 676), the prosternal process and metasternal cavity being 
very conform in the two. A. cephalotes seems to have only the two basal joints of 
the male tarsi clothed with sexual pubescence beneath, while in Agabus cordatus 
there are distinctly three joints so clothed. A. maderensis is a specis of imperfect 
form, but its thorax is very nearly as broad as the base of the elytra. 
The prosternal process and metasternal cavity in the group are comparatively 
imperfect, and in Agabus intersectus the former terminates in front of the middle 
coxee and is not received into the metasternal cavity. 
It is probable that the species will ultimately be separated to form as many dis- 
tinct groups or genera; all the species (with the exception perhaps of A. cephalotes) 
seem to be excessively rare, so that I have hada good deal of difficulty in ascer- 
taining their characters, and have as yet only very imperfectly succeeded. 
Group 2. 
Outline of thorax slightly discontinuous, or continuous, with that of elytra ; 
prosternal process comparatively broad, nearly flat, evenly and distinctly margined, 
shining and impunctate ; metasternal groove moderately broad. Hind coxe never 
large; wings of the metasternum large ; coxal lines deeply impressed in their upper 
part, much prolonged in the anterior and outward direction ; hind legs slender or 
moderate (never thick) the femora little thickened, their postero-external angle little 
obtuse, sometimes rectangular. Male front feet but little developed, clothed beneath 
with very short ‘‘glandular” pubescence ; sexual differences of sculpture slight. 
The species comprised in this group show a good deal of difference in various 
points. Dytiscus guttatus, appears to approach the first group by the comparatively 
ill-fitting base of the thorax and elytra; while the latter species, by their more 
perfect form, shorter swimming legs, polished surface and more highly developed 
metasternal groove, approach the two following (8rd and 4th) groups. Agabus 
hypomelas is a somewhat exceptional species, for although greatly resembling D. 
guttatus, it has the prosternal process slightly raised along the middle, and feebly 
punctate. 
