9SA On Aquatic Carnivorous Coleoptera or Dytiscidce. 



and in groups 7 and 8 of the genus Agabus, they are scarcely present, there being 

 merely a few punctures grouped close together in a manner approximating to 

 rectilinear, and each bearing a very obscure short hair or cilia. ^Yhere the swim- 

 ming legs are highly developed (comp. Agabus, group 4), the punctures become 

 confluent so as to form a regular line or depression, in which are placed the thick, 

 contiguous, and regularly arranged cilise. In all cases however, including even 

 those species where their development is rudimentary, the cilise are placed so as to 

 form at their insertion a kind of linear depression parallel with and approximate to 

 the hind border of the femur at its outer extremity. 



The width of the ventral side pieces is subject to some degree of variation, but 

 so far as I have been able to examine the character, the variation is not great ; and 

 it may be said that the width of the ventral side piece of the fourth segment 

 is about one -half or one-third of the length. 



The aggregate may be described as a really natural one, inasmuch as the definition 

 given of it will apply to no member of any allied group ; and also because that 

 the primary aggregates of which it is composed are closely linked together. 



There is still however doubt as to its being actually isolated, because if other 

 characters besides those above enumerated be taken into consideration, then a fresh 

 combination becomes possible. Moreover each of the characters reappears, or at 

 any rate is greatly approximated to, in allied groups. Thus the wide ventral side 

 pieces reappear in Scutopterus, {htij. op.) although the rest of the members of the 

 group with which that genus is associated (the Colymbetini) have the ventral side 

 pieces narrow. As an instance of an imjiortant character that is variable in the 

 group, but which has been left out of consideration by me, I may point out the 

 penultimate stigma ; this in Agabus is quite small, while in Colymbetini it is 

 transversely elongate. In Ilybius which I have included among Agabini, this 

 stigma is also transversely elongate to as great an extent as it is in certain 

 Colymbetini. 



C. J. Thomson, (and other naturalists have lollowed him in this), has made the 

 want of a setigerous space on each of the middle of the third, fourth, and fifth ventral 

 plates a distinctive character of the European Agabini, and has thus distinguished 

 the group from the Colymbetini, in which the setigerous pore is present in a high 

 degree of development. The character will not however bear when rigidly examined 

 so high a degree of taxonomic importance as that assigned to it by the talented and 

 most observant Swedish naturalist; for on careful examination it may be found 

 present in Agabini in various stages of development. Thus in Dytiscus bipustu- 

 latus (Agabus No. 751), a few scattered fine punctures bearing a very short hair may 

 be detected about the middle of these segments, and in Dytiscus fuscipennis (Agabus 

 No. 752) these punctures and setae are more highly developed, and are placed so 

 as to form a diffuse patch on each side of the middle of the segment : in Ilybius they 

 are present to a greater or less degree of concentration on the middle of the segment; 



