On Aquatic Carnivorous Coleoptera or Dytiscide. 849 
examined. The prosternal process is broad and short, in fact subtriangular, with 
the base of the triangle placed behind ; the point of junction with the prosternum 
is marked by a slight tubercular projection. The middle cox are rather broadly 
separated. The hind coxw are about twice as great in area as the metasternum, 
their upper border subparallel with the lower one, but still, near its outer termination, 
distinctly arched in front ; the hind coxal cavities are not contiguous, and possess a 
very distinct opening or coxal notch, and external to this there is a projecting 
portion (extra-rimal portion) of about equal width to that of the intra-rimal portion ; 
this extra-rimal portion conceals and protects the outer part of the articular cavity. 
The coxal lines are very fine, but a good deal divergent in their anterior part. The 
swimming legs are slender; their femora are slender, and are rounded at the 
extremity, their tibize and tarsi are very slender and very little ciliate, the latter are 
not compressed laterally,and are terminated by two small, slender, equal, curvedclaws. 
The front and middle tarsi are very short, four-jointed, the third joint imperfectly 
bilobed. The elytra have on their inner face a raised ridge, which is somewhat 
waved near the apex, but is not provided with any articular tongue; they have a 
genicular fossa at the shoulder, (or base of the epipleura). 
The sexual differences are found chiefly in the antennz and in the sculpture ; 
they are remarkable in a few species, but in the majority are inconspicuous ; it is 
probable that in some species dimorphism of sculpture occurs in the females, but 
I am not able to announce this with certainty. 
The aggregate is very widely distributed on the surface of the earth, but does 
not occur in the northern regions, and is unknown in New Zealand and the Pacific 
Islands. 
The species are very difficult to distinguish inter se, and moreover it is certain 
that only a small portion of those existing are known to me. Under these 
circumstances it would be useless to attempt any tabular discrimination of them : 
comparison of fresh individuals with those already named and described will be, in 
the present imperfect condition of our knowledge, the only trustworthy mode of 
determination. Anyone attempting to discriminate the species should note the 
nature of the margin of the front of the head, and examine carefully the structure 
of the antennze and tarsi. 
I. 18.—Genus QUEDA. (Vide p. 336.) 
‘A single species is isolated under this generic name. It isan insect somewhat simi- 
lar in form to the Hydrovati, but exceeds them in size. The characters are toa large 
extent similar to those of Hydrovatus ; but the head is completely rounded in front, 
and has a very evenly raised margin, and the labrum is so extremely concealed that 
on the most careful examination only the long fringes by which it is terminated, 
and its outer angles, can be detected. The coxal lines are subparallel, the coxal 
opening is broader and shorter, and the extra-rimal portion is broader and completely 
