During recent work on the coconut leaf moth, Agonoxena pyrogramma Meyr., in New Britain, Mr. R. W. Paine has found that this insect, whose larvae live in the leaflets of the coconut palm, is parasitised by a very small Tachinid fly which belongs in the genus Actia R.-D.; this same Tachinid was briefly alluded to as an unidentified dipterous parasite of Agonoxena pyrogramma by O'Connor (1954). The Actia species concerned belongs in the group of species in which the fifth wing-vein (M3 + 4) is setulose, and seemed on first examination to be almost indistinguishable from A. darwini Mall., an Australian species common in Queensland. However, examination of the male genitalia has shown striking differences from A. darwini and it is evident that a new, closely allied, species is involved; this new species is described below. Following the description I have given a key to the Indo-Australasian species of Actia in which the fifth vein is setulose, so that A. painei sp.n. can be placed.