On Aquatic Carnivorous Coleoptera or Dytiscidce. 933 



in Ilybiosoma though very indistinct they are still more aggregate ; in Colymbetes 

 gaudichaudi, (Leuronectes, No. 773), they are present in a very minute form, and in 

 Col. peruvianas (Agametrus, No. 776) they are quite concentrated into a fovea and 

 conspicuous, although not so large as in most Colymbetini. 



The Agabini are in their geographical distribution specially characteristic of cold 

 and temperate regions, both in the northern and southern hemispheres, but more 

 particularly in the northern ; and thence a few penetrate into neighbouring tropical 

 regions ; the group is unknown in New Zealand and the Pacific Islands, although 

 well represented in Australia; the few members found in South America, are 

 probably inhabitants of mountainous regions. 



II. 0. — (Seven unassociated genera.) 



The seven aggregates placed between the Agabini and Colymbetini, are distin- 

 guished from these two groups, by the fact that they do not possess the accumulation 

 of cilise at the angle of the hind femur as found in the Agabini, and that the 

 stigmatic rugae of the Colymbetini are also absent. As these are both purely neo-ative 

 characters, and as in many other respects these aggregates differ much from one 

 another, it seems to me that they cannot naturally be considered to form an 

 associated group ; at any rate I must decline the responsibility of treating them as 

 such at present. 



As regards the other characters made use of by me in the synthesis of the 

 components of Agabini and Colymbetini, there are some observations that should 

 be made in order to show the kind of variation these characters undero-o in these 

 unassociated genera. 



The setigerous punctures of the lower face of the femur exhibit some most 

 interesting peculiarities. In Copelatus they appear to be entirely absent, and the 

 lower face of the femur shows a smooth impunctate surface. In Lancetes on the 

 other hand there is an elongate sei'ies of setigerous punctures placed just on the 

 middle of the lower face of the femur, that is about equidistant from its front and 

 hind margins, at some distance from the base, and not extending to the outer 

 extremity ; these punctures are seven or eight in number and vary in minor details 

 of situation and development. In the other genera they are nearly entirely absent 

 but whenever they can be traced it will be seen that they are placed, not near the 

 hind border of the femur as in Agabus, but on the middle of its longitudinal axis, 

 that is to say on a line drawn from base to apex of the femur at equal distances 

 from its front and hind border. Thus in Lacconectus three or four obsolete 

 punctures bearing each a very fine seta may be detected on the middle axis near 

 the apex, and in addition to them one or two others extending towards the hind 

 angle. 



The ventral side pieces in all these seven genera are more or less intermediate 



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