1. In this paper five species of Simulium and 16 species of Austrosimulium are dealt with.
2. The new genus Austrosimulium differs mainly from the former in the number of joints in the antennae, which are ten instead of eleven; it seems to be restricted to the Indo-Australian region.
3. In many cases the species of Austrosimulium cannot be differentiated from each other in the adult stage, although they are perfectly different in their early stages and especially in the pupal stage.
4. Seven species of Austrosimulium occur in New Zealand: A. vexans, Mik, A. ungulatum, sp. n., A. australense, Schin., A. tillyardi, sp. n., A. longicorne, sp. n., A. multicorne, sp. n., A. laticorne, sp. n. Only the first two of these are distinguishable from the others in the adult stage; the remainder can only be differentiated in the pupal stage or the late larval stage.
5. Five out of these seven New Zealand species are known in their early stages.
6. In Australia (including Tasmania) five species of Simulium and nine of Austrosimulium are known to the writer, i.e.: S. aurantiacum, sp. n., S. fergusoni, sp. n., S. ornatipes, Skuse, S. umbratorum, sp. n., S. terebrans, sp. n., A. crassipes, sp. n., A. cornutum, sp. n., A. tasmaniense, sp. n., A. victoriae, Roub., A. furiosum, Skuse, A. bancrofti, Taylor, A. torrentium, sp. n., A. simile, sp. n., A. weindorferi, sp. n.
The two species A. victoriae, Roub., and A. furiosum, Skuse, have not been identified with certainty, so that further investigation may show that one or two of the new species are synonymous with them.
7. The early stages of one species of Simulium and five of Austrosimulium from Australia are here described.