In the typical genus of this family we have some of the largest known Hemiptera, measuring up to 3 inches in length and broad in proportion. They are aquatic, generally living in still waters, feeding on small fish which they capture with their stout spined legs; they play havoc with the small fry in a pond, and are popularly known in consequence as “Fish-killers.” The body is broad, but flattened on the dorsal surface, coming to a rounded point at the apex; the well developed wings are folded beneath the horny elytra; the whole shape being well adapted to the life they lead. In summer time they often leave their ponds, and, attracted by the light, come flying to the windows. _Belostoma indicum_ has a wide range from Southern India to Australia; it measures slightly under 3 inches in length, and is of a uniform dark brown colour. The large curved beak bent under the head, projecting eyes, and great spined fore legs show its carnivorous propensities; the middle and hind legs are fringed with delicate swimming hairs, and terminate in a pair of fine claws. Unlike most of the other aquatic hemiptera, the abdomen terminates in an oval tip without any anal appendages. Sharp speaking of this family (Insects Pt. II. p. 567) says: “In the waters of the warm regions of the continents of both the Old and New Worlds they are common insects, but as yet they have not been found in Australia.” However, Mayr records it from Australia, “Die Belostomiden 1871” (Verh. Z. C. Gesell, Wien); and I have a specimen from Port Darwin, Northern Territory, and also a number of specimens from Southern Queensland. _Sphaeroderma equis_ is a curious oval-shaped water-bug that crawls about among the mud and water weeds in water-holes and creeks; it has a very wide range, probably all over Australia; the female has the curious habit of carrying her eggs stuck upon her back in a regular sheet covering the whole of the elytra. It is of a uniform shining brown colour, and measures ¾ of an inch in length; the head is smaller than that of _B. indicum_, with the eyes not so prominent and angular. Family 13. Back-Swimmers. NOTONECTIDAE. These water-bugs have oval convex bodies and always swim with the belly upwards; their eyes are very large, situated on the sides of the head, the latter inserted into the prothorax, which overlaps it. The front legs are shortest, the fore tarsi not flattened but furnished with two claws. Their bodies are provided with long hairs which enable them to carry an air supply about with them. They are very active insects, and can be often observed in our water-holes and ponds swimming beneath the water, or coming to the surface and raising the tip of the body to obtain a fresh supply of air, when they can be easily captured with a hand net.