In 1864 Dr. Schiner estimated that the number of described Australian Diptera was 1056, including those which he described (Diptera des Novara), collected by Frauenfeld in the neighbourhood of Sydney during the visit of the Austrian Frigate. In a long series of papers reaching from 1859 till just before his death in 1892 Bigot described a great many species (among them some from Australia) chiefly in the Annales de la Societé Entomologique de France. The only systematic Australian work is Skuse’s “Monograph of the Australian Diptera” (Pro. Linn. Soc. N.S.W. 1888–90), which however was never completed, dealing only with the NEMATOCERA comprising the Culicidae, Tipulidae, Cecidomyidae and some of the smaller families. There is no complete catalogue of Australian Diptera, but I have been greatly assisted in my work on this family through the identification of my specimens by Mr. Coquillett of Washington. Family 1. Gall-Gnats. CECIDOMYIDAE. This is an extensive family of small delicate midges with long slender antennae composed of many bead-like segments beautifully feathered with whorls of hairs. The abdomen is stout at the base, short and tapering to the tip; the legs are long and slender without spurs; the wings are clothed with fine hairs that easily rub off, and furnished with very few longitudinal veins, and in some genera only one cross nervure. They are known as “Gall-gnats,” or “Gall-flies,” and though the habits of the larvae are very diverse, some living under bark, others in animal matter, and a few predaceous or even cannibalistic in their habits, the majority of them are found in plant tissue and produce malformations or regular well defined galls, often of very remarkable structure, upon the foliage or twigs of their food plant. The egg is deposited in or under the bark, epidermis of the leaf, or frequently in the flower buds of plants, the irritation caused by the active larvae producing the aborted tissue. These larvae are very easily recognised if examined with a lens after they have been extracted from the gall, as they are furnished with a “breast bone,” an anchor shaped process that stands out very distinctly in the centre of the ventral surface and is unknown in the larvae of any other gall-producing insect. Through the discovery of Wagner, a Russian entomologist, that the larva of a Cecidomyia produced young; also through the curious exudations of the larvae and pupae of others which are sometimes called “flax seed” from their shape; and the very destructive habits of several species which damage the wheat, like the Hessian Fly in America, this family has received a great deal of attention. Over 1,000 species have been described from all parts of the world, and Australia is particularly rich in these insects. Skuse (Pro. Linn. Soc. N.S.W. 1888 and 1890) has described over 100 species and figured some of the most peculiar galls.