From the known species occurring in crocodilians, the genus Dujardinascaris is redefined and found to be a homogenous group of species, with dujardini Travassos, 1920 as the type species. The following new species are described and added to the genus: gedoelsti, puylaerti, waltoni, mawsonae and taylorae. The following species are excluded from the genus: vandenbrandeni, australiensis, tasmani, alata and antipini. The distribution of the species in Dujardinascaris is as follows: in African crocodiles—dujardini, madagascariensis, gedoelsti, and puylaerti; in South American caimans—longispicula, paulista, and chabaudi (possibly a synonym of paulista); in North American alligator–waltoni; in Crocodylus acutus—helicina; in the Indian gavial—woodlandi; in crocodiles in Papua New Guinea and Australia—mawsonae and taylorae.
These species are differentiated mainly by the relative length of the spicules and the form of the guber naculum in the males and by the relative length of the vagina and the form of the vulva in the females.