Two closely related species of swamp skink (Lissolepis coventryi and Lissolepis luctuosus) occur in Australia, one in the extreme southeast and the other in the southwest of the country. They are separated by more than 2,000 km of arid country, and they have been isolated from one another for a considerable period of time, possibly more than 20 million years. We investigated the gastrointestinal nematode fauna of each using preserved museum lizards. More than 80% of each species of lizard was infected with nematodes. Three new species of nematode are described; Spinicauda victoriae n. sp. occurs only in L. coventryi in the southeast and Spinicauda similis n. sp. only in L. luctuosus in the southwest, each occurring at a similar prevalence and intensity. Moaciria paucipapillata n. sp. occurs in both populations. Abbreviata antarctica also occurs in both populations, though infrequently in L. coventryi. Pseudorictularia disparilis was present in 14% of L. coventryi, attesting to the aquatic habitat this lizard. The close similarity of the two species of Spinicauda, which differ only in the form of the eggs, indicate a common ancestry. The presence of A. antarctica adults in these semi-aquatic hosts supports the suggestion that this morphologically variable species originated in a cool, damp environment and has adapted to a wider range of hosts and to a less-humid environment. The cestode Oochoristica vacuolata was recovered primarily from L. coventryi.