On Aquatic Carnivorous Coleoptera or Dijtiscidce. 96S 



FOUHTH SYNTHESIS (SERIES). 



IV. 1. — Dytisci fragmentati. 



The first aggregate of this synthesis consists of a few more or less fragmentary 

 aggregates, viz., one aggregate of the first degree (Pelobius), one aggregate of the 

 third degree (NOTERIDES), and two aggregates of the second degree (Vatellini 

 and Laccophilini) ; these together form the first series Dytisci fragmentati. 



A single point of structure binds together these aggregates into a series, viz., 

 that the metathoracic episternum does not penetrate to the middle coxal cavity, 

 this part being formed externally by only three species — a portion of the middle 

 piece of the mesosternum, the extremity of the mesothoracic epimeron and the 

 most anterior portion of the side of the metasternum. 



In other respects these four unequal aggregates are extremely different inter se ; 

 and it is therefore doubtful whether the arrangement of them together into a 

 single series is a really correct procedure, for the components have no other bond 

 of union than the one mentioned, and this it will be seen, is a negative as much 

 as a positive one. Moreover they do not really agree on this one point, for in 

 Pelobius, NOTERIDES, and Vatellini, the apex of the metathoracic episternum 

 is broadly separated from the coxal cavity, whereas in the Laccophilini this part 

 very nearly reaches the cavity — so nearly indeed that it requires a rather careful 

 examination to assure oneself on the point. At the same time these forms are all 

 of them quite different from any of those which compose the second seires, or 

 Dytisci Complicati, and in this sense the series is truly a natural one ; it is 

 indeed the case that the Vatellini, approximate, by the structure of their anterior 

 and middle tarsi, the tribe HYDROPORIDES of the second series, but the 

 approximation is only a general not a special one, and the whole of the Vatellini 

 have in common a most peculiar point of structure (the termination of the 

 prosternal process in front of the middle legs) which is only found in one or two 

 widely separated members of the HYDROPORIDES. And I have, therefore, 

 felt justified in establishing the Dytisci fragmentati as a distinct and natural 

 series. 



The first of the four aggregates of the series — Pelobius — is an altogether isolated 

 form, and in a natural classification should probably be j^laced among the Oarabidas 

 rather than in the Dytiscidse. 



The Noterides I have already alluded to as being evidently the fragmentary 

 remains of an assemblage formerly more extensive than it is at present, some of its 

 components are of low organization, while others have attained a great degree of 

 perfection in some of their special structures. 



TKANS. KOV. DUB. SOC, N.S., VOL. II. ( H 



