25 S 



On Aquatic Carnivorous Coleoptcra or Dytiscida. 



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 martrin of the wingf-case when this is closed : the inner portions of the 

 two coxaj, 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 tibioe and tarsi with elongate, depressable, swimming 

 hairs, and by a compression of the femora, tibire 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 I. — Dytisci Fragmentati. 

 Metathoracic episternum not reaching the middle coxal cavity; {vide below). 



Series II. — Dytisci Complicati [vide p. 317). 

 Metathoracic episternum reaching to the middle coxal cavity. 



IV. I. — 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- 

 guished as follows. 



Metasternum quite straiglit iu the~\ 



middle behind, and with a dis- I Drr/^DTTT-cr / •? n^n\ 

 ^. , , ' , , . yPELOBIvS (vide p. 2o9). 



tmct transverse suture marking I \ l / 



off a supplemental y piece. ) 



Metasternum more or less pointed ) 



in the midtUe behind, and not VNOTEEIDES (i-iWe p. 2G0). 

 marked by a transverse suture. j 



' Prostemal process not reaching the ) -TT- . ,,,, , ., „„.-.. 



. . ^ f- V ATELLiKi (vide p. 282). 



metastemimi. J \ l / 



L-nal process reaching the me- ) t / • ? n^^^ ^ 



^ " > Laccophilini (vide p. 286).* 



•mum. ) \ I / 



* In this group the metathoracic episternum very nearly reaches the middle coxa, while in the other 

 components of the series it is widely separated thei'efrom. 



Greatest anterior extension 

 of the hind coxa is near 

 the middle (longitudinally) 

 of the body. 



Greatest anterior extension 

 of the hind coxa is nearer 

 to the epipleura than to 

 the mesial line of the body 



Proster 

 tastemum, 



