248 On Aquatic Carnivorous Coleoptcra or Dijtiscidfp. 



ill the males of the Hydaticides both spurs are absent on the front legs. In the 

 Noterides the front tibias undergo a modification of form, which attains its 

 maximum of development in Suphis, where the tibia is changed in position owing 

 to a twisting of the leg, the front face being turned outwards ; the anterior spur 

 is developed into a thick, elongate, very curved, acuminate process, and being 

 apparently soldered to the tibia gives rise to the appearance of a hooked tibia : 

 the tarsus is inserted on the inner (now the lower) edge of the tibia just under a 

 large prominence. In other members of the Noterides modifications similar to 

 this may be traced, the most constant feature being the large curved anterior (or 

 lower) spur; the structure of the primitive Noteride tibia still exists in 

 Pronoterus, where we find a short very broad triangular tibia, with a rather small 

 strongly curved spur at its inner angle. A very highly modified front tibia is 

 found in the male of Eretes, where it is formed so as to allow of a maximum of 

 rotatory motion over the tarsus when this is firmly fixed. 



The anterior tarsi of the Dytiscidfe belong to three quite distinct types ; in one 

 of these they are five-jointed, the joints being more or less cylindrical and armed 

 beneath with spines, between which the surface is shining and polished ; the four 

 basal joints differing little inter se in length, the fifth more elongate ; this structure 

 is however greatly obscured in the males as these in many species have the three 

 basal joints dilated, sometimes enormously dilated, and clothed beneath with peculiar 

 hairs or cups ; the number of joints is however always distinctly five : the 

 Laccophilini, Amphizoa, Colymbetides, Dytiscini, Hydaticides, and Cybistrini 

 possess tarsi of this structure, which is in fact, except as regards the extreme 

 development in the males, that which exists in the Carabidte. The second type of 

 structure of the front tarsi is likewise a pentamerous or five-jointed one, and the 

 tarsi are spinose beneath, but they have the basal joint ver}'' much larger than the 

 others, and greatly comj^ressed laterally, that is to say the joint is very deep from 

 its upper surface to the sole, this latter being narrow ; this form of tarsus is peculiar 

 to the Noterides ; the male tarsi though often a good deal larger than those of the 

 female, are never highlj- modified, and they have only a very few cups on their 

 under surface. The third form of tarsus exhibits only four joints, and of these the 

 basal three are very different from the terminal one, being more or less broad and 

 flat so as to present beneath a flat sole, wdiich is without spines but bears a dense 

 spongy pubescence, the third joint is more or less deeply emarginate or bilobed, 

 while the fourth or terminal joint is slender and cylindrical ; the male feet are not 

 greatly different from those of the female, although frequently a good deal broader. 

 This form of tarsus is found in the Hydroporides and Yatellini, and is not only in 

 respect of the number of joints a tetramerous tarsus, but is essentially as regards 

 both the form and clothing of the joints similar to what exists in the Tetramerous 

 or Phytophagous (as opposed to the Carnivorous) Coleoptera. 



The modifications shown in the structure and development of the male tarsi in 



