On Aquatic Carnivorous Coleoptera or Dytiscide. 933 
in Ilybiosoma though very indistinct they are still more aggregate ; in Colymbetes 
gaudichaudi, (Leuronectes, No. 773), they are present ina very minute form, and ip 
Col. peruvianus (Agumetrus, No. 776) they are quite concentrated intoa 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 cilize at the angle of the hind femur as found in the Agabini, and that the 
stigmatic rugze of the Colymbetini are also absent. As these are both purely negative 
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 undergo 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 series 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 cr 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 
6D2 
