884 On Aquatic Carnivorous Coleoptera or Dytiscidce. 



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. 



Grol'p 19. 



Coxal Hues 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 in a 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, Lee, 

 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 chalconotus. Agabus subtilis and A. nigroseneus 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 Ilj^bius) and their claws 

 are rather stout and little curved, and unequal. 



Thus these species (D. vittiger, Agabus subtilis, and Agabus nigrogeneus) 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. subtihs 

 and A. nigroeeneus 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 

 w'idth 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 



