On Aquatic Carnivorous Coleoptera or Dytiseidce. 94.> 



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 Pronoterns 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 joint 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 mesosteruum 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 continuous 

 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 Dytiscidee, is found in water beetles of other families (Hydrophilidpe 

 and Gyrinidae) and is no doubt the morphological correlative of greater functional 

 jictivity 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 Dytiscida3. 



The increase in the area of the mesosternum is entirely due to growth in the 

 epistemum, which becomes very large, the epimeron not sharing in the least in 

 this inci'ease, 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 Dytiscidse, (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 

 metathoracic-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 tlie 



