The Genus _Gasteruption_, which takes the place of the Genus _Foenus_ in the earlier catalogues, contains 36 described species from Australia; as they are rare insects, there are probably many more to be discovered. Nothing is known about their habits for certain, but they are supposed to be parasitic upon the larvae of wood boring insects; I have generally found them flying round the trunk of a dead or burnt tree. They differ from the former genus in having the head almost globular, with antennae standing out straight in front, and large oval eyes on the sides; the thorax is more elongate, rounded in front, so that the insect appears to have a slight neck. The abdomen springs from a rounded node on the thorax, with the basal segments slender, swelling out gradually, and broadest at the tip; the females bear a very long hair-like ovipositor. The legs are slender, the hind pair longest, with both the thighs and apical half of the tibiae thickened in a very distinctive manner. Ten species are described from Sydney; and one, _Gasteruption pedunculatum_, is also common to New Zealand. The Genus _Aulacus_ contains ten described species of smaller insects. _Aulacus apicalis_ is parasitic upon the larvae of a longicorn beetle (_Piesarthrius marginellus_). I have found as many as fifty, each enclosed in a thin parchment cocoon, all matted together in a single cavity. This little wasp has a long extended ovipositor, and measures about ½ an inch in length; the head and greater portion of the abdomen is black, the rest reddish brown, with a blotch of yellow on the upper surface of the base of the abdomen; the hyaline wings are tipped with black. Family 12. Long-tailed Wasps. MEGALYRIDAE. These remarkable parasitic wasps, peculiar to Australia, are comprised in a single genus containing 16 species, none of which are very common. They are all shining black insects; the head short, broad and almost rounded, the thorax broad and stout, both very rugose and clothed with fine silvery hairs on the sides; the eyes large, circular, and very prominent; ocelli small; the antennae composed of irregular wiry joints; the wings semitransparent, generally banded with black, and the transverse nervures wanting in the apical half; legs long, with the thighs thickened. The abdomen is closely attached to the thorax, cylindrical, tapering to the extremity, and in the females furnished with an ovipositor often more than three times the whole length of the insect, looking exactly like three black horse-hairs. These elongated ovipositors are used for depositing their eggs in the wood-boring larvae of longicorn beetles belonging to the Genus _Phoracantha_, and probably others of like habits, which feed under the bark in the sap wood of different eucalypts. The perfect insects are generally found about flowers on low shrubs in summer.