_Mutilla rugicollis_, described by Westwood many years ago, is our largest species, measuring in the larger female over ¾ of an inch in length. She is black, very deeply punctured, thickly clothed with black and silvery white hairs, the latter forming white patches on the hind portion of the head, sides and under-surface of the abdomen, and has a dorsal row of five distinct spots down the back. The male is much smaller, with somewhat similar but not so distinct white markings, and is furnished with dark brown wings, which are hyaline, close to the sides of the thorax. _Mutilla quadrisignata_ has about the same measurements as the female of the last species; with blackish hairy covering, except on the under surface of the abdomen, and four dark, reddish brown, oval spots forming a square on the dorsal surface. Both these species have a wide range over Australia. _Mutilla ferruginata_ is a smaller species with a similar deeply punctured surface; is of a uniform dull rusty red colour, thickly clothed with darker brown hairs; the legs and antennae deeper coloured than the body. _Mutilla cordata_ is typical of the smaller active forms that frequent tree trunks; the male is black with dark wings and slender abdomen, and measures about ⅓ of an inch in length; in this case much larger than the female, which has a rounded body with the centre of the dorsal surface occupied with a large rounded golden blotch. I have found the best time to collect these insects is in the hottest part of the day, when they are running up and down the larger tree trunks; but they are very active, and drop at the least alarm, so that it takes some practice to capture them. Family 15. Flower Wasps. THYNNIDAE.