882 On Aquatic Carnivorous Coleoptera or Dytiscidce. 



punctate ; luetasternal £p.'oove imperfect ; swimming legs elongate, slender and 

 feeble ; hind coxae rather small, but wings of the metasternum not large. 



I am obliged to place these species isolated from the other groups ; the imperfect 

 structure should place them near to group 1, and to Agabus hypomelas, (the 

 first species of group 2) but the anterior claws of the male are elongate ; while 

 by the rounded sides of the thorax they approach the twelfth group, from which 

 they differ by the scarcely compressed prosternal process, and the less obscure 

 metasternal groove. 



Group 12. 



Prosternal process small, much compressed ; middle legs very approximate so 

 that the metasternal groove between them is rudimentary and obscure. Sides of 

 thorax rounded. Coxal lines rather deep and a good deal divergent in front. 



These four species seem to form a natural group on account of the above peculi- 

 arities ; the hind coxEe are short and their upper border but little arched, and the 

 wings of the metasternum are not short, though in this respect the species do not 

 closely agree inter se. The swimming legs are long and feeble. 



Agabus altaicus, Gebl., of the nineteenth group has a quite similar form of the 

 prosternal process and metasternal groove, but the coxal lines are very different. 



Group 13. 



Prosternal process acutely raised or carinate along the middle, but its sides little 

 depressed, so that it is not compressed, the sides evenly and distinctly margined ; 

 metasternal groove well developed ; swimming legs elongate, rather slender ; wings 

 of metasternum large (D. confinis) or moderate (Agabus infuscatus) ; male front 

 tarsi little incrassate, their claws elongate. 



These two species are readily distinguished from all others by the acutely carinate 

 prosternal process. 



Group 14. 



Hind coxaj large, with acutely arched upper border ; wings of the metasternum 

 very short; prosternal process rather small ; smmming legs rather slender. Male 

 tarsi but little incrassate. 



These two species are associated together because of the very short wings to the 

 metasternum ; in some other respects they are very different, Dytiscus femoralis 

 has a very small prosternal process which is much compressed, and an extremely 

 narrow metasternal groove ; Dytiscus abbreviatus has a moderately large prosternal 

 ])rocess, and it is not compressed, but is somewhat carinate along the middle, and 

 its metasternal groove is better developed. 



Group 15. 



Sides of thorax very feebly margined, not at all curved. Prosternal process very 

 flat, not visibl\- margined ; metasternal groove rather elongate; wings of metasternum 



