FAM. 47. HETEROCERIDAE.—_Labrum and mandibles projecting forwards; antennae short, the terminal seven joints broad and short, forming a sort of broad serrate club; legs armed with stout spines; tarsi four-jointed._ The Heteroceridae are small beetles covered with very dense but minute pubescence; they live in burrows among mud or sand in wet places, and are found in many parts of the world. They possess a stridulating organ in the form of a slightly elevated curved line on each side of the base of the abdomen, rubbed by the posterior femur. The larvae live in the same places as the beetles; they have well-developed thoracic legs, the mandibles are porrect, the three thoracic segments rather large, and the body behind these becomes gradually narrower; they are believed to eat the mud amongst which they burrow. We have seven British species of Heteroceridae. FAM. 48. PARNIDAE.—_Prosternum distinct in front of the coxae, usually elongate, behind forming a process received into a definite cavity on the mesosternum; head retractile, the mouth protected by the prosternum. Tarsi five-jointed, terminal joint long._ {244}Although the characters of these Insects are not very different from those of Byrrhidae, of Dascillidae, and even of certain Elateridae, there is practically but little difficulty in distinguishing Parnidae. They are of aquatic habits, though many, in the perfect state, frequently desert the waters. There are about 300 or 400 species known, but the family is doubtless more extensive, as these small beetles attract but little notice. There are two groups:—1. Parnides, in which the front coxae have a considerable transverse extension, the antennae are frequently short and of peculiar structure, and the body is usually clothed with a peculiar, dense pubescence. 2. Elmides, with round front coxae, a bare, or feebly pubescent body, and simple antennae. _Parnus_ is a genus commonly met with in Europe, and is less aquatic in habits than its congeners; it is said to enter the water carrying with it a coating of air attached to its pubescence. Its larvae are not well known; they live in damp earth near streams, and are said to much resemble the larvae of Elateridae. _Potamophilus acuminatus_ has a very interesting larva, described by Dufour; it lives on decaying wood in the Adour. It is remarkable from the ocelli being arranged so as to form an almost true eye on each side of the head; there are eight pairs of abdominal spiracles, and also a pair on the mesothorax, though there are none on the pro- or meta-thorax; each of the stigmata has four elongate sacs between it and the main tracheal tube; the body is terminated by a process from which there can be protruded bunches of filamentous branchiae. The larvae of _Macronychus quadrituberculatus_ is somewhat similar, though the features of its external structure are less remarkable. The Elmides live attached to stones in streams; the larva is rather broad, fringed at the sides of the