$58 On Aquatic Carnivorous Coleoptera or Dytuscide@. 
swimining legs of the male are more powerful, as are also often all the other legs ; 
the front and middle tarsi are frequently dilated; these tarsi are also often compressed 
laterally and rarely are quite flat on the upper surface: the anterior trochanters 
in the male are frequently the seat of incomprehensible secondary sexual characters, 
in some species scarcely to be detected, while in others they are carried to an 
extent that may almost be called ludicrous. 
The peculiar structure of the front tarsi readily leads to any water-beetle | 
possessing it being identified as a member of this aggregate. In no other Dytiscide 
is the terminal joint of the front tarsus so little exserted from the third joint ; this 
is so remarkable that in the females of some species of the genus the tarsi have the 
appearance of being only three-jointed. 
The dark marks on the elytra are formed by lines placed in the longitudinal 
direction, but of irregular lengths, and much united together in the transverse 
direction so as to give somewhat the appearance of highly irregular transverse 
bands; the marks so formed rarely extend so far as the outer margin which is thus 
nearly always paler than the sutural portions. 
' The genus isin several respects approximated by Hyphoporus of the Hydroporini. 
Hyphydrus is distributed over the whole of the Eastern hemisphere, except the 
colder parts thereof; in the Western hemisphere it has only been found in New 
Caledonia. 
I. 31.—Genus STERNOPRISCUS. (Vide p. 384.) 
Ten species form this aggregate ; their individuals are of small size, and of 
moderately elongate form; the punctuation of the upper and under surfaces is very 
dense, and the colour more or less variegate. The sexual differences are often 
extreme. The thorax has a longitudinal plica on each side. The prosternal process is 
elongate and slender ; the middle coxz are absolutely contiguous, and their exserted 
apices project beyond the level of the body; the fork of the mesosternum is elongate, 
and the prosternal process which extends over the middle coxe is thus rendered 
peculiarly protuberant. The hind coxe are elongate externally. The hind coxal 
cavities are not contiguous, but each has an internal prolongation, by means of 
which the basal portions of the two swimming legs are allowed very nearly to meet. 
The coxal lines are short, but rather acutely elevated, distinctly turned outwards 
near the apex, forming a rather acute coxal process, with a small coxal border. 
The swimming legs are slender, their tibize are slender at the base, and near the 
base have a crook or distortion, which is more conspicuous in the males than in the 
females. The front and middle tarsi are distinctly five-jointed : the mesosternum 
is placed at a very obtuse angle with the metasternum and thus is quite visible. 
The genus is very easily distinguished by the distinctly 5-jointed tarsi, and the 
comparatively ill-constructed and fitted together parts of the mesosternum and 
adjacent pieces. It has points of similarity with widely separated forms, and has 
