Systematics of Nanexila Winterton & Irwin, gen. nov. (Diptera : Therevidae) from Australia

Nanexila Winterton & Irwin, gen. nov. is described and figured from Austral ia. This genus of typically small, slender flies is divided into three spec ies-groups following cladistic analysis. The previously unplaced N. manni ( Hardy) comb, nov, is redescribed in the Nanexila manni species-group, along with four new species: N. armeniacum, N. carminata, N.furcata and N. nana. Nanexila ruficornis (Macquart) comb. nov. is redescribed in the Nanexila p alassa species-group, along with ten new species: N. argentiquadris, N. cyl omelasma, N. danielsi, N. ligula, N. lignyos, N, livea, N. palassa, N, spil otis, N. variabilis, and N. vittata. Four new species are described in the Nanexila atricostalis species-group: N. atricostalis, N. aureilineata, N. i ntermedia, and N. paradoxa. The twenty Nanexila species and dye outgroup sp ecies were compared across 167 states in 71 characters. A cladistic analysi s was conducted and the phylogenetic relationships of Nanexila discussed. N anexila is endemic to Australia, with a largely southern distribution. Only N. argentiquadris and N. cylomelasma are known from northern Australia. Ad ult Nanexila have been collected between August and April, with the peak pe riod of activity for most species during October and November. The duration of adult activity is related to latitude, with northern species active for longer periods than southern species.