884 On Aquatic Carnivorous Coleoptera or Dytiscide. 
Group 18. 
Swimming legs highly developed, short and incrassate ; prosternal process rather 
broad, but a good dea} compressed ; wings of metasternum moderately large ; male 
front tarsi much incrassate, furnished beneath with rather long hairs bearing rather 
well developed palettes, claws rather short. 
The powerful swimming legs of the single species, suggest a comparison with 
Dytiscus brunneus (group 4), but there is no evidence of other approximation 
between the two. 
Group 19. 
Coxal lines in their anterior part but little directed outwards. Prosternal process 
rather broad but always compressed ; wings of metasternum large, or moderate. 
Male tarsi and claws variable. 
The essential character of this group is that the coxal lines are different in their 
direction in their anterior portion, to what they are in the other groups, being 
more abbreviate and having a less outward prolongation ; in the other groups 
these lines have their anterior parts sensibly prolonged so that they join the front 
border of the coxa ina gradual manner, forming a most acute angle: in this 
group they either do not join the front border of the coxa at all, or do so in such 
a way as to form a very considerable though still acute angle. 
The group however includes some very discrepant forms. Agabus discors, Lec., 
has the metasternal groove extremely rudimentary, the front feet of the male bear 
beneath an abundant elongate sexual clothing, but this bears no palettes, and the 
claws are very elongate. In Dytiscus vittiger the metasternal groove is narrow 
and ill developed, the male tarsi are poorly developed as regards both incrassation 
and the claws and the sexual clothing: this species has the hind claws rather stout 
and distinctly unequal, and the hind margins of the outer sides of the joints of the 
hind tarsi are slightly lobed in their lower parts. A. altaicus agrees with D. 
vittiger in the narrow imperfect metasternal groove, but in other respects accords 
with Dytiscus chaleonotus. Agabus subtilis and A. nigrozeneus are peculiar in 
the male characters, this sex having the basal joint of the hind tarsus with the 
lower external edge margined, (approximating group 1 of Ilybius) and their claws 
are rather stout and little curved, and unequal. 
Thus these species (D. vittiger, Agabus subtilis, and Agabus nigrozeneus) appear 
to make an approach to Ilybius in the hind feet, but in different directions; D. 
vittiger approximating by this character to the second group of Ilybius; A. subtilis 
and A. nigrozeneus to the first group. 
The other species of the group are more homogeneous, but still they show consider- 
able discrepancies in the claws and sexual clothing of the male tarsi, and also in the 
width and length of the metasternal groove. 
The group not only approximates to Ilybius in two directions as above indicated, 
but also by D. vittiger and A. altaicus approximates group 12 of its own genus 
