On Aquatic Carnworous Coleoptera or Dytiscide. 913 
It is a perfectly distinct one, and would be very homogeneous, were it not for 
Dytiscus liberus (No. 1,084), which departs considerably from the other species. Itis 
smaller than the other species, less convex, and has no black markings on the head 
and thorax as the other species have ; it has moreover the middle legs more slender, 
and their tibize less spinulose, and the antennal portion of the head shorter, and 
the setze of the middle femora shorter. In some of these points it makes an approxi- 
mation to Rhantaticus. Some of the other species likewise depart more or less in 
their structure from the average, thus Nos. 1,085, 1,086 and 1,087, have the front 
border of the hind coxa not so near the middle one as the other species have: and 
Hydaticus austriacus (No. 1,085), differs from the other species by the simple 
middle tarsi of the male. 
I. 75.—Genus HRETES. (Vide p. 699.) 
Two closely allied species are all that exist to form this very distinct aggregate. 
The shape and colour are peculiar, and the skeleton is much softer than in most 
other Dytiscide. Rather flat above, and rather narrow, the insect is a good deal 
narrowed towards the front, the outlines of the thorax and elytra are very discon- 
tinuous, and the eyes large and prominent. The whole insect is of a pale yellow, 
or whitish colour, the head and thorax have two or three, inconstant (sometimes 
absent) transverse dark markings, and the elytra are more or less densely marked 
with very distinct isolated punctures, each of which is black, and there may be a 
transverse irregular black fascia before the apex: this is siuate so that the suture 
projects slightly there. The head in front of the eyes is extremely reduced. The 
prothorax has a very fine elevated lateral margin. The prosternum is very reduced 
in front of the coxee, but the inter-coxal portion is much thickened, the prosternal’ 
process in which it terminates is rather narrow, gradually acuminate towards the 
apex, and obsoletely margined. ‘The hind cox are enormous, so that the meta- 
sternum which is elongate in the middle, is reduced at the sides to a very short, 
parallel-sided, curved lacinia or wing, which is greatly deflexed round the anterior 
border of the coxa, and is a little dilated near its rounded termination ; this termina- 
tion is placed far from the epipleura, and the coxa is prolonged behind it and the 
metathoracic episternum as far as the epipleura, while intervening between the edge 
of the epipleura, the outer hinder edge of the episternum and the upper terminal 
border of the coxa, there is seen very distinctly a triangular piece, which is a portion 
of the metathoracic epimeron left uncovered by the very reduced epipleura: the 
posterior margin of the coxa becomes thickened in a peculiar manner near its termina- 
tion, so as to mark off the outer portion asa triangle separated from the larger 
part by a thickened raised line: the coxal lines are fine, short and abbreviated in 
one, obsolete in the other species ; the coxal lobes, are very short, rather broad, 
without supra-articular border. The hind legs are rather slender, their tarsi are 
elongate, the basal joint being not greatly shorter than the tibia, they are terminated 
