258 On Aquatic Carnivorous Coleoptera or Dytiscide. 
metasternum, and actually forming a considerable portion of the part of the skeleton 
placed between the middle and hind legs, extending at the sides so as always to 
reach the margin of the wing-case when this is closed: the inner portions of the 
two coxee, connected accurately together along the mesial line of the body by a 
straight suture of considerable length, so that the middle of the base of the 
abdomen (or hind body) is largely separated from the true extremity of the 
metasternum. 
The posterior legs modified for swimming, though in an extremely variable 
degree, by the ciliation of the tibize and tarsi with elongate, depressable, swimming 
hairs, and by a compression of the femora, tibie and tarsi, by which these parts 
become less cylindric, but broader and flatter. 
Posterior tarsi always five-jointed ; the anterior and middle ones either four, or 
five-jointed. The family as known to me comprises nearly twelve hundred species, 
arranged in two series, Viz. :— 
Series 1.—Dytisci Fragmentati. 
Metathoracic episternum not reaching the middle coxal cavity ; (vide below). 
Series I].—Dytisci Complicati (vide p. 317). 
Metathoracic episternum reaching to the middle coxal cavity. 
IV. 1.—Dytisci Fragmentati. 
The episternum of the metathorax does not penetrate so far towards the middle 
of the body as to reach the middle coxal cavity, but is separated therefrom by a 
process of the mesothoracic epimeron which articulates with the side wing of the 
metasternum. 
Four divisions of very different values, and very distinct inter se can be distin- 
euished as follows. 
Metasternum quite straight in the 
middle behind, and with a dis- PELOBIUS (vide p. 25 9). 
Greatest anterior extension tinct transverse suture marking 
of the hind coxa is near off a supplementary piece. 
the middle (longitudinally) 
of the body. Metasternum more or less pointed 
in the middle behind, and not - NOTERIDES (vide p. 260). 
marked by a transverse suture. 
( Prosternal process not reaching the 
Greatest anterior extension 
Z metasternum. 
of the hind coxa is nearer 
to the epipleura than to 
the mesial line of the body. 
\ Varentint (vide p, 282). 
Prosternal process reaching the me- 
tasternum. \ LAccOPHILINI (vide p. 286).* 
* In this group the metathoracic episternum very nearly reaches the middle coxa, while in the other 
components of the series it is widely separated therefrom. 
