They are distinguished from the last family (which they resemble in the earlier stages of their development) in having very short antennae; the fore-legs much longer than the two hind pairs; and in having the eyes on either side divided, thus having two eyes looking down into the water and two above, so that they can see both sides at the same time, an admirable adaptation of vision for beetles living so much on the surface of the water and liable to be attacked from above or below. The tip of the body is not covered by the elytra, and when diving downward they carry a bubble of air attached to the extremity. These beetles are well represented in Australia, and have been described by Clark previously mentioned, Regimbart (Annals Soc. Ent. France 1882), Macleay (Trans. Ent. Soc. N.S.W. 1871), and Boisduval in the “Entomology of the voyage de l’Astrolabe.” Our common species about Sydney, _Macrogyrus canaliculatus_, is of the usual boat-shaped form, silvery black, with the wing covers finely striated; it measures about ½ an inch in length. _M. oblongus_ is a somewhat smaller species not so broad in form; is browner, and the wing covers are very slightly striated; it is also found in the vicinity of Sydney. _M. paradoxus_ was described and figured by Regimbart from Australia with no exact locality, but I have collected it on the North West coast of Australia, and seen others from Southern Queensland, so that it has a wide range. It is not much over ¼ of an inch in length; is dark olive; the outer margin is dull yellow, and it has a few fine striae on either side of the elytra. I have found the pupae of one species, probably _M. oblongus_, in clay cells attached to a bit of board on the bank of a waterhole in the western country of N.S. Wales. Family 5. Clubbed-horned Water Beetles. HYDROPHILIDAE. This family is also known under the Group _Palpicorna_ in reference to the clubbed antennae, and made to include a second family, which are very closely allied but are terrestial in their habits. These beetles have five jointed tarsi; short clubbed antennae, with the palpi slender and much longer than the antennae. Most of the beetles are vegetarian in their diet, though many of them in the earlier stages of their existence are carnivorous. These are the largest of the Water Beetles; and the typical species are ovate and very convex in form; the thorax very broad; the tibiae slightly spined on the edges, terminating in a stouter spine at the apex; the tarsi ciliated. They are poor swimmers when compared with the two last groups.