(Sp) 
Or 
bo I 
On Aquatic Carnworous Coleoptera or Dytiscida. 
I. 29.—Genus DARWINHYDRUS. (Vide p. 373.) 
This name represents an autogenus, known only by asingle individual; it is an 
insect of small size, of peculiar broad rounded form, with a rather flat upper surface 
and costate elytra. The head is rounded and margined in front; the swimming legs are 
slender and rather short ; the epipleurz of the elytra become gradually narrower 
from the base to the apex ; by this character it departs from the other Hyphydrini, 
and approximates to Hydroporus nebulosus, &c. (gen. Chostonectes) of Australia. 
This insect was recorded in Castlenau’s collection as being from Capetown; I 
consider however there is just a possibility it may really be from Australia. 
I. 30.—Genus HYPH YDRUS. (Vide p. 374.) 
About five-and-twenty species at present form this aggregate. The size of the 
individuals is rather uniform, varying between 33 and 6 m.m. of length; the form 
is short, broad, and very elevated, the convexity being chiefly on the undersurface. 
The upper surface is nearly always variegate in colour, by means of black marks on a 
yellowish or brownish ground. Head rounded in front and margined, labrum not 
visible from above, exserted and visible from beneath. Prosternal process short, not 
truncate behind, somewhat variable in size and form, its apex not received into a 
groove on the inter-coxal portion of the metasternum: middle coxe nearly 
contiguous ; the inter-coxal process of the metasternum is curved upwards at its 
termination to touch the process of the mesosternum, and this perpendicular portion 
is slightiy hollowed in adaptation to the back (or upper) part of the prosternal 
process. Metasternum elongate in the middle, with excessively short side wings 
which are greatly deflexed down the outer portion of the hind coxe. Hind coxe 
enormous, their anterior border excessively arched ; coxal processes adpressed, their 
outer terminal angle obtuse or rounded ; the articular cavities, are therefore quite 
distinctly separated and are not at all protected, but (on the leg being extracted from 
the articulation) are seen to be entirely exposed externally to the coxal process : first 
ventral segment not soldered to coxe. Elytra on their inner face near the apex of 
their raised ledge with a highly developed elongate tongue, which is received into 
a pocket on the internal face of the lateral piece of the penultimate segment. 
Swimming legs rather slender ; their tibize and tarsi rather strongly ciliate, the 
latter on both upper and under edge ; terminated by a rather stout, little curved 
claw, and with an excessively short and indistinct second claw. Front and middle 
tarsi four-jointed, the fourth joint short, protruding but little from the groove at the 
apex of the third joint in which it is inserted, the third joint large, the fourth 
inserted at a great distance from its base. 
The sexual differences are often very striking, the females being often smaller 
and weaker with quite different sculpture: as regards this latter point the females 
are dimorphic in some species, certain individuals resembling the males: the 
