On Aquatic Carnivorous Coleoptera or Dytiscide. 945 
a wonderful manner, and firmly fixed at its base in a cavity at the back of the 
tibia, so as to become rigid and immobile, and appear as if it were a prolongation 
of the extremity of the tibia; in Notomicrus and Hydrocoptus, the modification ot 
the leg scarcely exists, but in Pronoterus the early stage of such an evolution may 
be seen in the fact that one of the two spurs at the apex of the tibia is a little 
elongate and curved. The male front tarsi are modified in a highly peculiar 
manner in some of these much evoluted forms, the basal jomt being greatly 
incrassate, and of peculiar form, while the following joints are in comparsion very 
little modified. 
The modifications of the male legs are carried to the greatest extent in Noterus, 
and it would appear that the evolution of the front limb in that genus has been 
principally subject to a sexual direction, while in Suphisini the very great modi- 
fication is subject only to very slight sexual disparity, and probably corresponds to 
some vital operations common to the two sexes. 
The mesosternum in the Noterides shows a great range of development, and in the 
higher forms its size and position is unusual amongst the water beetles ; in Hydro- 
canthini and still more in Noterini, instead of being articulated to the metasternum 
almost at right angles therewith, it is placed in a plane more or less contmuous 
with that of the metasternum; this is not the case in Notomicrus; but in Synchortus 
this continuity of the meso- and metasterna is carried to its extreme, so that these 
two parts are but little discontinuous in their plane ; at the same time the area of 
the mesosternum becomes larger than usual; this development of the mesosternum, 
rare in the Dytiscidze, is found in water beetles of other families (Hydrophilidee 
and Gyrinide) and is no doubt the morphological correlative of greater functional 
activity of the intermediate legs; these no doubt take a greater part of the 
locomotive activity in Noterides than they do in the other tribes of Dytiscidee. 
The increase in the area of the mesosternum is entirely due to growth in the 
episternum, which becomes very large, the epimeron not sharing in the least in 
this increase, .but rather becoming smaller and more linear. This diminished size 
of the mesothoracic epimeron is one of the characteristics of the Noterides, but it 
is found in other Dytiscide, (especially is some members of Bidessini) and cannot be 
used for distinguishing or defining the Noterides as suggested by Crotch. In no 
case however, so far as I am aware, except in the Noterides, is it accompanied by 
an increase in the episternum; the epimeron, even in Notomicrus, where the 
characteristic structure of the Noterides is so rudimentary, is small in comparison 
to the episternum. The angle of the epimeron which touches the angle of the 
inetathoracic-episternum is but little conspicuous, and very obtuse ; and owing to 
the enlargement, above described, of the episternum, the epimeron at this point is 
much diminished in breadth ; these characters although developed to a less extent 
in Notomicrus are yet extant in it, and the Noterides may be correctly defined as 
possessing a mesothoracic epimeron of very small area in comparison with the 
