The several families included in this group comprise a number of aquatic or semi-aquatic bugs. The GALGULIDAE, known as “Sand-bugs,” are curious little creatures distinguished from the others in having ocelli. They are very short and broad in form, with projecting eyes, and in general appearance each suggests a miniature crab. They have short four jointed antennae situated below the eyes, and are furnished with legs well adapted for running on the ground. They are found on the edges of swamps or creeks, and feed upon different kinds of small insects. In colour they are usually of a uniform dull brown to black; the upper surface is generally much roughened. Never moving unless touched, they trust to their sordid colours to escape detection, for as they match the ground so well, they are difficult to find. _Mononyx annulipes_, one of our commonest species, is about ¼ of an inch in length; is of a uniform dirty brown tint, with the legs and under surface dull yellow; the body is very rugose and fringed on the outer edges with fine bristles. Montandon has described several other Australian species (Bulletin, Societé des Sciences, Roumania, 1899). The NEPIDAE are popularly known as “water scorpions” on account of the curious tail appendages projecting from the tip of the abdomen. They live in ponds, and feed upon different water insects, attaching their eggs to the leaves of the plants. They have the wing covers folded closely over the back protecting the wings from the water, and fly rapidly from pool to pool when the water dries up. There are many species found in Australia, most of which have a wide range. _Rantara varipes_, under 1 inch in length, has a tail about as long again as the body, and is of a light yellowish brown colour. It might be likened to a mantis, with its slender form and fore pair of legs furnished with spines on the inner edges to hold its prey. The other legs are long and slender with curved claws at the extremities. In the Genus _Nepa_ the insects have the head and body flattened; the elytra cover the wings; the abdomen is broadly rounded at the extremity, terminating in a pair of long slender bristles. The beak curved under the head is large and stout; the eyes are large, the fore legs are spined, and the other legs furnished with a pair of slender curved claws. _Nepa tristis_, measuring about 1 inch to the tip of the body, is of the usual form and dull brown colour, with the upper surface of the abdomen showing bright red when the wings are expanded. It is found in the bottom of ponds crawling about among the weeds. Family 12. Fish-killers. BELOSTOMIDAE.