The two pentastomid species currently included in the genusLeiperia Sambon, 1922 (family Sebekidae Fain, 1961) are re-assessed. Measurements of chitinous structures, notably the hooks, fulcra and oral cadre of three adult females of the otherwise well-characterised speciesL. cincinnalis Sambon, 1922, from the bronchi of the Nile crocodileCrocodylus niloticus, exhibit a degree of variation that is usual in pentastomid morphometrics. Similar measurements of six nymphs from the aorta and heart of two other crocodiles, although equally variable, do not differentiate these from infective nymphs removed from cysts within the body cavity of a South African fish (Pelamatachromis robustus) intermediate host. Adult females of another species,L. australiensis n. sp., from the bronchi of the Indopacific crocodileCrocodylus porosus from Northern Australia are described. Females (N=3) are smaller and more slender than their African counterparts, and their chitinous structures, although equally variable, are correspondingly smaller. A mature male, from the lung of Johnston's crocodileC. johnsoni, is also allocated to this species because the ranges and diet of the two crocodilian hosts overlap. Also, this zone of syntopy is sufficient to maintain populations of two other species belonging to the family Sebekidae (Sebekia spp.) in both hosts. This male is the first of the genusLeiperia to be fully described, and its copulatory spicules are quite distinctive. Three other immature specimens ofL. australiensis from the lung, or near to the lung, of the definitive host are also described. In the light of these findings the literature is re-appraised, and it is evident that at least two moreLeiperia spp. exist in South America, and that presently these are known only as nymphs. The existing South American species,L. gracilis Heymons & Vitzthum, 1935 (=Pentastoma gracile Diesing, 1835) was established only on the basis of immature or nymphal forms, almost certainly encompassing several genera. Despite claims to the contrary in the literature, this ‘species’ should be regarded as aspecies inquirenda. Aspects of the life-cycle ofLeiperia spp., from the infective stage in fish and the subsequent instars, are also discussed.