Abstract
Iridophora clarki gen. nov., sp. nov., Megaselia sembeli sp. nov. and M. kodongi sp. nov. are described. The females of I. clarki attack the workers of the ant Iridomyrmex cordatus (Smith). The same ant species is also attacked by M. sembeli, and the morphology of this species indicates that it is close to P. beirne Brues, the typespecies of the genus Plastophora. The loss of the type-material of the latter species prevented synonomy of the genus when it was re-evaluated (Disney, 1978). The detailed examination of M. sembeli now indicates that the genus Plastophora is a synonym of Megaselia (syn. nov.). A consequence is that P. dubitata Brues, 1935 becomes a homonym of M. dubitata (Malloch, 1912) and the replacement name M. bruesi nom. nov. is proposed. The females of M. kodongi attack workers of a species of Pheidologeton which forages on the forest floor. The habit of Iridomyrmex cordatus in using covered ways up trees appears to be related to its extreme vulnerability to attack by these two phorides.