828 On Aquatic Carnivorous Coleoptera or Dytiscide. 
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 with 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 produced 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 coxz (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 laminz of the hind coxee 
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 
laminz ; 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 1s covered by 
the wing-case, and is smooth and shining so as to be greatly differentiated from the 
main part; the epimeion is entirely membranous. 
The hind coxe 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 lamine 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 limit 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 
*Schiodte (Danmarks Eleutherata, p. 414) has proposed to separate Pelobius from all other Dytiscide 
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). 
