Terebratuloids have a sporadic distribution in the Australian Permian rocks, but at some localities they are abundant. Two distinct provinces, an eastern and a western, are recognised. The eastern is dominated by the genera Gilledia SteWi and Fletcherithyris nom. novo pro Fletcherina Stehli; less abundant genera are Maorielasma Waterhouse, Marinurnula Waterhouse, Glossothyropsis Girty, Pseudodielasma Brill, and Jisuina Grabau. The last three genera are represented by a few specimens only, and are of little zoogeographical significance. The only other area in which similar faunas are known is New Zealand. The western province is dominated by Hoskingia gen. nov., but it also has representatives of Fletcherithyris, Gilledia, and Yochelsonia Stehli. The abundance of Hoskingia indicates possible relationships with the Tethyan and Uralian provinces, though the absence of the Notothyris group shows that there was no open migration from these areas. This distribution supports other evidence of a climatic difference between eastern and western Australia at this time. The group is of interest stratigraphically. The genera Maorielasma and Marinurnula, and the species of Gilledia, Fletcherithyris, and Yochelsonia, are all short-ranged. Many of the species are restricted to single basins. An attempt is made to provide a consistent terminology for the internal plates of terebratuloids, and a theoretical discussion of the homologies of these plates is given. It is shown that despite previous assertions to the contrary, punctation density can be a taxonomically useful feature in the group. In the systematic section the new Family Gillediidae and Subfamily Gillediinae are established, together with the new Genus Hoskingia of the Subfamily Dielasmatinae. In addition to the genera mentioned above, Beecheria Hall and Clarke is discussed in detail. The status of the long established species RhYllchonella' inversa de Koninck, Gilledia jervisensis (Etheridge), and G. cymbae/ormis (Morris) is considered, and it is shown that they cannot be adequately interpreted at the present time. The species Fletcherithyris amygdala (Dana), Hoskingia trigonopsis (Hosking), Hoskingia nobilis (Etheridge), and Yochelsonia thomasi Stehli, are redescribed. It is shown that Terebratula biundata McCoy is a synonym of F. amygdala (Dana). New species of Fletcherithyris, Hoskingia, Yoche/sonia, Gilledia, Maorielasma, and Marinurnula are described.
