Ordovician limestones with fossil shells occur in the Leigh's Creek District in South Australia, and also at Tempe Downs and Petermann and Laurie's Creeks, W. of Alice Springs. The euomphaloid shell _Ophileta gilesi_ was described from Laurie's Creek, and _Eunema larapinta_ from the Tempe Downs. A pleurotomarid, _Raphistoma browni_ (Fig. 98) occurs near Leigh's Creek, and at Laurie's and Petermann Creeks. A Pteropod, _Hyolithes leptus_, has been described from the Lower Ordovician of Coole Barghurk Creek, near Meredith, Victoria. =Silurian Gasteropods.--= The Silurian Gasteropods are fairly well represented, especially in the upper stage, and are widely distributed throughout the Australian fossiliferous localities. Moreover, some of the species are identical with those found as far off as North America and Europe. In Victoria the shales and sandstones of the lower stage (Melbournian) contain the genera _Bellerophon_, _Cyrtolites_ and _Loxonema_. The Pteropoda include _Tentaculites_, _Coleolus_, _Hyolithes_ and _Conularia_ (_C. sowerbii_ (Fig. 99 F), a species also found in Great Britain). The Victorian limestones and mudstones of the upper stage (Yeringian) are somewhat rich in Gasteropods, such genera occurring as _Pleurotomaria_, _Phanerotrema_ (with cancellated shell and large slit-band), _Murchisonia_, _Gyrodoma_, _Bellerophon_, _Trematonotus_ (a spiral shell with a large trumpet-shaped mouth and a dorsal row of perforations in place of a slit-band), _Euomphalus_, _Cyclonema_, _Trochus (Scalaetrochus)_, _Niso (Vetotuba)_, _Loxonema_, _Platyceras_ and _Capulus_. The section Pteropoda contains _Tentaculites_, _Hyolithes_ and _Conularia_. [Illustration: =Fig. 99--SILURIAN GASTEROPODA.= A--Hyolithes spryi, Chapm. Silurian (Melb.) Victoria B--Gyrodoma etheridgei, Cressw. sp. Silurian (Yeringian). Vict. C--Bellerophon cresswelli. Eth. fil. Silurian (Yeringian). Victoria D--Euomphalus northi, Eth. fil. sp. Silurian (Yeringian). Victoria E--Trochonema montgomerii. Eth. fil. sp. Silurian. Tasmania F--Conularia sowerbii, Defr. Silurian (Yeringian). Victoria ] In the Silurian of New South Wales the chief Gasteropod genera are _Bellerophon (B. jukesi)_, _Euomphalus_, _Omphalotrochus_, and _Conularia (C. sowerbii.)_. In Tasmania are found _Raphistoma_, _Murchisonia_, _Bellerophon_, _Helicotoma_, _Trochonema_ and _Tentaculites_. =Devonian Gasteropods.--= The derived boulders of the White Cliffs opal field have been referred to the Devonian system, but of this there is some doubt, as the Gasteropods noted from these boulders closely resemble those of the Silurian fauna: they are _Murchisonia Euomphalus_ (_E. culleni_), and _Loxonema_. The genus _Murchisonia_ has also been recorded from the Baton River, New Zealand (Wangepeka Series) by MacKay. The Middle Devonian Gasteropod fauna in Victoria, as found in the Buchan and Bindi Limestones, comprises _Murchisonia_, _Trochus_, and _Platyceras_.