These are small homoptera, in appearance suggesting miniature cicadas. The head is generally broader than long, sometimes deflected and with large eyes; the ocelli are three in number, the lateral ones situated on the summit of the head close to the hind margins of the eyes, and the central one at the apex of the median suture. The antennae are each composed of ten joints, the first two shorter and thicker than the following ones, and the terminal joint surmounted with two short bristles. The thorax is broad, with well developed tegmina and wings, and like the aphids both pairs might properly be called wings. The venation is simple, constant, and useful in the work of classification. They are formed for jumping, with a spine-like process on the coxa of each hind leg, and the apex of the tibiae of the hind legs furnished with a row of short fine spines. The tarsi are two jointed, terminating in a pair of large claws. [Illustration: =Fig. 160.=--Diagram of Psylla (_Thea opaca_) ♀. Showing the structure and venation of the wings. 1_a_, Face lobes; 2_a_, prothorax; 3_a_, mesanotum; 4_a_, dorsulum; 5_a_, scutellum, tegmina; 1_b_, costal nervure; 2_b_, primary stalk; 3_b_, clavus; 4_b_, clavical suture; 5_b_, stalk of sub-costa; 6_a_, stalk of cubitus; 7_b_, sub-costa; 8_b_, lower branch of cubitus; 9_b_, upper branch of cubitus; 10_b_, lower fork of lower cubitus; 11_b_, stigma; 12_b_, upper fork of the lower branch of cubitus; 13_b_, radius; 14_b_, lower fork of upper cubitus; 15_b_, upper fork of upper cubitus. 3, Genitalia ♂; 4, Genitalia ♀; 5, Head of _Spondyliaspis eucalypti_, showing face lobes. (Pro. Linn. Soc. N.S.W.)] The female lays her eggs in clusters on the twigs or foliage, from which the curious, little, large-headed larvae emerge, and, after undergoing a series of moults during which they develop large wing-pads on the shoulders and more joints in the antennae, they finally come forth, perfect four-winged insects. They take their family name from _Psylla_, a flea, given them by Linnaeus in reference to their jumping powers, and their popular name of “Lerp Insects,” from the habit of the larvae of many species of forming “lerp scales,” shell-like protective coverings formed from exudations from the insects. Other species cover themselves with flocculent matter after the manner of mealy bugs; and yet another group form regular oval or rounded galls on the foliage. They are found in most of the warmer parts of the world, and are very numerous in Australia, where they seem to take the place of the APHIDAE to a certain extent; they are readily collected in all stages of growth upon their food plant, and can be easily bred.