Cethegus fugax is a species of mygalomorph spider in the family Euagridae . It is endemic to Australia. It was first described in 1908 by French arachnologist Eugène Simon.
The species occurs in South Australia and Western Australia, in low woodland and open forest habitats, on sandy and gravelly soils. The type locality is Lion Mill (now Mount Helena, a suburb of Perth).
The spiders are fossorial, terrestrial predators. They construct sheet webs against rocks, logs and stumps.