The members of the Genus _Pterodontia_ have the body inflated like a bladder; we have several species in Australia, generally found resting on twigs or tree trunks. _Pterodontia mellii_ measures under ½ an inch in length; the thorax and body are swollen out like a bladder; it is of a general black colour, with a mark on the back, the fore legs, and a large blotch on either side of the body bright ochreous yellow; but the dark portions are thickly clothed with fine black downy hairs like a bumble bee. The wings on account of the swollen body look much smaller than they really are. I have specimens from Queensland, and Hunter River N.S.W., and they probably have a wide range. _Panops flavipes_ is a very curious looking fly from Moruya, N.S. Wales, measuring over ½ an inch in length; it is of a general dark bronzy black tint thickly clothed with fine down, silvery on the tip of the abdomen. The head is very small, black and shining, with the thickened cylindrical antennae standing out in front; the thorax, swollen out behind the head, has a large angular white patch on either side; the abdomen not quite as thick as the thorax is deeply corrugated. The wings have the front half deeply clouded and the hind portion transparent. _Acrodes fumatus_ is a much smaller species about ⅕ of an inch in length; the head and thorax are black; the bladder shaped abdomen is tawny yellow, with parallel stripes of black down the centre and sides, and transverse white bars at the apex of each segment. They were collected in numbers about Cook’s River, near Sydney. Family 10. Mydas Flies. MYDAIDAE. These might be called “mimic flies,” because, with their large thickened antennae (often swollen out into a compressed club at the tips), their broad heads, elongated bodies, and bright variegated black and yellow markings, they can be very easily mistaken at first sight for Pompilid wasps. The mimicry is further emphasised by the thickened spined legs, and coloured wings. We have a number of species in Australia; they are allied to the “Robber-flies” which some of them resemble. The larvae of foreign species are predaceous, feeding upon the grubs of various wood-boring beetles. _Mydas fulvipennis_ has the greater part of the head, thorax, under surface of the abdomen, and thighs black; with the face, antennae, legs, wings and rest of the abdomen except two indistinct narrow bars, bright reddish yellow. It measures over ¾ of an inch in length, and is of the usual elongate robust form with long clubbed antennae and thickened legs. My specimens come from Southern Queensland. [Illustration: Plate XXVIII.--DIPTERA. Family MUSCIDAE. 1. _Chaetogaster violacea_ (Macq.). Family TABANIDAE. 2. _Pangonia guttata_ (Donov.). 6. _Pangonia auriflus_ (Donov.). 14. _Tabanus abstersus_ (Walk.). 7. _Lamprogaster laeta_ (Guérin). Family ASILIDAE.