FAM. 7. PELOBIIDAE.—_Antennae destitute of pubescence: outer lobe of maxilla jointed, metasternum with a short transverse impressed line on the middle behind. Hind legs rather slender, formed for swimming, the tarsi longer than the tibiae._ This family is limited to the one genus _Pelobius_ (_Hygrobia_ of some authors). Like _Amphizoa_, to which it is in several respects analogous, it has a singular geographical distribution; there are only four known species, one lives in Britain and the Mediterranean region, one in Chinese Tibet, two in Australia. _Pelobius_ may be briefly described as a Carabid adapted to a considerable extent for living in and swimming about in water; differing thus from _Amphizoa_, which has no special adaptation for swimming. The larva of _Pelobius_ is remarkable; it breathes by means of branchial filaments on the under surface of the body, the spiracles being present, though those of the abdomen are very minute and the others small. The head is very large, the mandibles are not tube-like, the food being taken after the manner of the Carabidae; the 8th abdominal segment ends in three long processes; the small 9th segment is retracted beneath them. The adult _Pelobius tardus_ is remarkable for its loud stridulation. The sound is produced by an apparatus described correctly by Charles Darwin;[91] {209}there is a file on the inside of the wing-cases, and the Insect turns up the tip of the abdomen and scrapes the file therewith. The Insects are called squeakers in the Covent Garden market, where they are sold. [Illustration: Fig. 95—_Cnemidotus caesus._ England. A, Imago; B, larva, highly magnified. (After Schiödte.)] FAM. 8. HALIPLIDAE.—_Antennae bare, ten-jointed; metasternum marked by a transverse line; posterior coxae prolonged as plates, covering a large part of the lower surface of the abdomen; the slender, but clubbed, hind femora move between these plates and the abdomen._ The Haliplidae are aquatic, and are all small, not exceeding four or five millimetres in length. The ventral plates are peculiar to the Insects of this family, but their function is not known. The larvae are remarkable on account of the fleshy processes disposed on their bodies; but they exhibit considerable variety in this respect; their mandibles are grooved so that they suck their prey. In the larva of _Haliplus_, according to Schiödte, there are eight pairs of abdominal spiracles, but in _Cnemidotus_ (Fig. 95, B), there are no spiracles, and air is obtained by means of a trachea traversing each of the long filaments. The Insects of these two genera are so similar in the imaginal instar that it is well worthy of note that their larvae should be distinguished by such important characters. Haliplidae is a small family consisting of three genera, having about 100 species; {210}it is very widely distributed. We have 13 species in Britain, all the genera being represented.