On Aquatic Carnivorous Coleoptera or Dytiscidce. 857 



I. 29.— Genus DARWINHYDRUS. {Vide p. 373.) 



This name represents an autogenus, known only by a single 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 epipleurae 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 HYPIIYDRJJS. {Vide p. 374.) 

 About five-and-twenty species at present form this aggregate. The size of the 

 individuals is rather uniform, varying between 31 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 coxae nearly 

 contiguous ; the inter-coxal process of the metasternum is curved upwards at its 

 termination to touch the process of themesosternum, and this perpendicular poi'tion 

 is slightly 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 coxas. Hind coxse 

 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 coxae. 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 tibiae 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 



