876 On Aquatic Carnivorous Cclcoptcra or DytiscidiB 



as ill Metronectes. The unique species is found in Corsica, and must rank as a low 

 form ; on the whole its nearest systematic ally is the Agabus cephalotes, which also 

 is peculiar to Corsica. 



I. 46.— Genus AGABUS. {Vide p. 493.) 



This is a very extensive aggregate, comprising no less than ninety -five species -. 

 the size is moderate, varying from 6 to 12 m.m. of length, the colour is usually 

 sombre, but in a few species is variegate, and a brassy tint of the upper surface is 

 not uncommon, the sculpture of the wing-cases nearly always consist of a fine reticula- 

 tion ; the meshes formed being variable in size and shape according to the species; 

 the terminal j oints of the palpi are not, or scarcely, broader than the preceding ones ; 

 hind coxae never extremely large ; wings of metasternum externally generally of 

 moderate length, but in a few species, very short, and parallel sided. Epipleurse of 

 elytra narrow behind the middle ; coxal lines always present, never greatly 

 approximated, (in A. serricornis, however, much more approximated than normally) 

 divergent in front, coxal lobes well formed, with distinct border. Swimming legs 

 often slender, never very highly developed, their femora, with setigerous patch (often 

 ill developed) at the postero-externo angle, their tarsi with the lower parts of the 

 hind margin of the basal joints not lobed, i.e., not produced so as to considerably 

 overlap the following joint), their claws simple, equal, and more or less curved. 



The above characters are drawn up to define a large number of species showing 

 great variety in parts of their structure, but all possessing the characters alluded to, 

 which is not the case Avith any of the allied aggregates. 



I have sought in vain to arrange the ninety-five species in separate aggregates, 

 but have failed in doing so, and have been obliged to content myself with arranging 

 them in twenty-three groups, to each of which I have assigned, as will be seen, 

 characters drawn from all such parts of the structure as I have been able to observe. 

 There are other characters to be found which 1 have not used, owing chiefly to my 

 not being able to examine them in the numerous cases of species where I have only 

 a single individual for study. Such are the structure of the inner face of the wing- 

 cases, and that of the various abdominal stigmata. The amount of variation of 

 structure shown by the aggregate will be gathered by an examination of the 

 characters I have mentioned as defining the various groups. C. J. Thomson (in his 

 Skandinaviens Coleoptera, Vol. I, and Opusc. Ent. VI), has established several 

 genera which I have not been able to adopt ; in doing this he has pointed out a 

 number of structural characters of great value, but he has unfortunately relied 

 largely on one which is very unsuitable for the purpose of arriving at a natural 

 classification ; I am alluding to the size and form of the wings of the metasternum; 

 so variable is this character that scai'cely any two species can be found exactly 

 agreeing as to it, and on the other hand, species which are nearly or quite conform- 



