On Aquatic Carnivorous Coleoptera or Dytiscida. 963 
FOURTH SYNTHESIS (SERIES). 
IV. 1.—Dytisci fragmentati. 
The first aggregate of this synthesis consists of a few more or less fragmentary 
ageregates, viz., one aggregate of the first degree (Pelobius), one aggregate of the 
third degree (NOTERIDES), and two aggregates of the second degree (VATELLINI 
and Laccopuiuint) ; these together form the first series Dytisei 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 Varenuint, the apex of the metathoracic episternum 
is broadly separated from the coxal cavity, whereas in the Laccopuitint 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 Varrnuit1 
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 im 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 placed among the Carabidee 
rather than in the Dytiscide. 
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. 
TRANS. ROY. DUB. SOC., N.S., VOL. II. 6 H 
