828 On Aquatic Carnivorous Coleoptera or Dytiscidce. 



The mesosternum is rather short, and although placed at an evident angle with 

 the plane of the metasternum, is very distinctly displayed between it and the 

 prosternum. The episternum is very large in comparison \\ ith the epimeron, this 

 latter being sub-linear, that is but little broader at its upper angle (or point of junc- 

 tion with the angle of the metathoracic episternum), which is very broad and rounded 

 and very indistinct, its inferior portion penetrates to the middle coxal cavity ; the 

 lower portion of the metasternum is prominent, and forms a rather narrow moderately 

 deep fork for the accommodation of the prosternal process. 



The metasternum is short, the middle portion of it is pi'oduced in front so as to 

 form an inter-coxal process which is much depressed in front, for the reception of 

 the prosternal process; the inter-coxal process, although elongate, does not attain the 

 fork of the mesosternum, and the middle coxae (when the prosternum is taken off) are 

 absolutely contiguous, and their cavities largely confluent; the posterior edge of the 

 metasternum in the middle is connected with the internal laminae of the hind coxae 

 by a transverse suture, and in front of this is marked by another transverse suture' 

 which connects at the outer border of the pyxal process with the one just mentioned, 

 so that a conspicuous supplementary piece exists at the front of the internal coxal 

 laminae ; the episternum is large, and although broad at its anterior part, does not 

 penetrate to the middle coxal cavity, its apex in fact is widely separated therefrom ; 

 the posterior portion of the episternum is narrow, the upper edge of it is covered by 

 the wing-case, and is smooth and shining so as to be greatly differentiated from the 

 main part; the epimeron is entirely membranous. 



The hind coxae are of very peculiar shape; each is longest at the internal lamina, 

 the outer portion being but short ; the greatest anterior extension of the coxa is 

 near the mesial line of the body, in fact close to the outer border of the interior 

 lamina, and external to this point the suture between coxa and metasternum proceeds 

 outwards in very nearly a direct transverse line, which however slightly inclines 

 backwards, till near its outer termination where it curves distinctly forwards to join 

 the apex of the episternum : the internal laminae are closely and accurately conjoined 

 with one another for their whole length by a perfectly straight, very distinct suture; 

 outwardly they are abruptly defined and limited by a fine raised coxal border which 

 extends their whole length, at the extremity each is marked by an elongate deep 

 notch, in which the articular process of the trochanter moves, and which in fact forms 

 the hmit of its motion towards the middle line of the body, so that the coxal cavities 

 are conspicuously and rather widely separated. 



The visible ventral segments are six in number; the basal one is greatly inter- 

 rupted in the middle for the accommodation of the pyxal processes, the suture be- 

 tween the second and third is peculiar,* it is quite distinct at the side, and curves 



*Scliiodte (Danmarks Elentlierata, p. 414) Las proposed to separate Pelobius from all other Dytiscidse 

 on account of this point of structure ; but this is quite impossible, for in the Hydroporides the character 

 reappears to a greater or less extent {vide Dytiscus duodecimpustulatus. Fab., in the genus Deronectes). 



