In the Moths of Victoria Visual Key for Oxycanus (Part 6) the images of the female antennae for O. australis and O. dirempta are shown right alongside each other. In both species the rami are very short, However I think this is O. australis because the segements are shorter, more triangualr in shape and the rami themselves are longer, like sawteeth. In O. dirempta the segments are longer, tubular with only very short rami. Also. yoor image is so sharp it also shows long, extremely fine hairs which I have not seen mentioned anywhere.