A number of our common species are plentiful on the flowering Leptospermum and Melaleuca bushes, and many of the smaller ones may be found feeding upon the honey dew covering the foliage of small eucalypts that are infested with scale insects. _Thynnus variabilis_, our commonest species, is a very handsome wasp measuring over ¾ of an inch in length, and nearly 1¾ across the outspread wings; the general colour is brown; the front of the head, hind margin of thorax, and broad bands or double dots across the abdominal segments bright yellow; the semiopaque wings reddish brown. The female, very broad in proportion, is shorter than the male; she is reddish brown; the abdominal segments are rugose and blotched with yellow, forming transverse bars of rounded dots on the hind portion. The antennae are short and curled; the head broad, with a stout thorax; and she has short hairy legs. _Thynnus leachellus_, slightly smaller, is found in the vicinity of Sydney. The abdomen is broader and shorter in proportion; the general tint is black, richly marked on the head and thorax with bright yellow, and each of the abdominal segments carries a narrow transverse band of the same colour, broken by a dorsal stripe of black. The female is much smaller, short and thickset; is of a general reddish brown colour; the abdomen is marked with yellow blotches and bands, only the last one divided as in the male. _Thynnus flavilabris_, somewhat larger, is quite black, with only the face marked with deep yellow; the wings are dark, smoke-coloured; and the hind margin of the thorax is thickly covered with white hairs. _Thynnus brenchleyi_ is a type of the North Australian forms; it is nearly as large as _T. variabilis_, but has the whole upper surface smooth and shining, the hind margin of the thorax and the base of the abdomen truncate and fitting close against each other. The head and prothorax are bright yellow, the rest black. This handsome insect was described by Smith in the Zoology of the Voyage of the Curaçoa, and it was said to come from the northern coast of Western Australia; my specimens were taken near Charters Towers, North Queensland. A female, sent with this species as its mate, is black, marked on the head, sides of thorax, and abdomen with yellow, and is furnished with a curious fringe of pale buff hairs on the hind margin of the thorax, and along the front of the first abdominal segment. In the Genus _Rhagigaster_ the males are more slender in form; the abdomen, elongated and deeply constricted or corrugated at the junction of the segments, is usually black, with more or less dark coloured wings: the females are very small in proportion.