On the Lystrosaurus zone and its fauna with special reference to some immature Lystrosauridae

In the past, collecting from the middle Beaufort Beds or Lystrosaurus zone has been badly neglected by field workers mainly due to the monotonous occurrence of the genus Lystrosaurus. Collecting has mostly been undertaken in such areas as the Harrismith Commonage, Oliviershoek Pass, Bergville or where there was a good possibility of finding either Thrinaxodon, Glochinodontoides or other faunal remains more exciting than lystrosaurus. In outline the Lystrosaurus zone follows more or less the same pattern as the main Karroo Basin and the Stormberg series with the shape of a "heel" in the Cradock, Middelburg, and Naauwpoort districts, roughly straightening out towards Bethulie from where the width of the outcrops becomes narrower through the Orange Free State and Natal. From a point in the Sneeuwberg Range, at Compass Berg, the zone can be followed to Middelburg, Naauwpoort, to the south east of Colesberg, on to Venterstad, Bethulie, Smithfield, Dewetsdorp, Thaba N'chu, Winburg, Senekal, Bethlehem and the Harrismith districts. In the Harrismith-Bezuidenhouts Pass area the Lystrosaurus zone is overlain by an outlier of the Stormberg series, but it appears again on the Natal side in the Oliviershoek Pass, Bergville and Estcourt districts; it can thence be followed to the west of Nottingham Road to Impendle, Bulwer, Cedarville, Umtata, Cathcart, Tarkastad and Cradock districts and back to Compass Berg. In the Rhenosterberg Range to the west of Middelburg, Cape, the lystrosaurus zone reaches a thickness of 1,000 feet, while in the Naauwpoort-Carlton Siding area a thickness of 1,200 feet was measured. From Naauwpoort the zone thins out considerablv towards Venters tad and Bethulie where it is reduced to an overall thickne;s of about 500 feet. It persists at this thickness through the Orange Free State and Natal, but increases again to about 800 feet in the Tarkastad and Cradock districts. There is no definite marker such as a consistent band or layer of sandstone anywhere between the top of the preceding Cistecephalus zone and the base of the Lystrosaurus zone, but there is a marked change in colour of the shales, mudstones and sandstones. At the base of the Ly strosaurus zone the shales and mudstones are normally greenish-grey in colour, above which they alternate with bright coloured reddishmaroon and purple shales and mudstones, with a light bluish-grey medium grained to almost coarse grained felspathic sandstone. In comparison the dark bluish-green shales of the Cistecephalus zone occasionally alternate with red and