388 THE SILURIAN RUGOSA OF THE YASS-BOWNING DISTRICT, N.S.W. By Dorothy Hill, M.Sc, Ph.D., University of Queensland. (Plates xi-xiii; four Text-figures.) \ [Read 28th August, 1940.] In this paper eighteen species of Rugosa already described from the Yass-Bowniug district are revised, and two genera and four species are described as new. Discussions are included of the families and genera involved. The age indicated by the Rugosa is Silurian, probably Upper Wenlock (Wenlock Lime-stone), and perhaps also Lower Ludlovian. The Rugosa were collected chiefly from two localities, (1) Yass River, at Hatton's Corner, near Yass, and (2) Derrengullen Ck. and its tributary Limestone Ck., near Bowning. The lithological succession at both these localities has long been known; most of the corals have already been described by Etheridge, and some have more recently been revised by Jones. At Hatton's Corner, the Bowspring Limestone, up to 100 feet thick, is overlain b}^ the Barrandella shales (about 70 feet thick), and these are followed by the Hume Limestone (20 feet). Further shales overlie the Hume Limestone, and are in turn overlain by the Phacops bed of very impure limestone of Rainbow Hill (Shearsby, 1912). For the Bowning district, the following succession at Bowning was given by Mitchell (Sussmilch, 1922, p. 36): Conglomerates at top (tuffaceous matrix). Shales and sandstones. Conglomerates. Shales and sandstones ) Shales, sandstones, conglomerates \ '■^-^PPer Trilobite Bed. Shales, i.e. Great Shale (Graptolites on west). Limestone, impure (with trilobites), i.e. Middle Trilobite Bed. Shales (with corals and crinoids), i.e. Lower Trilobite Bed (Graptolites on east). Limestones (corals, brachiopods). Grits at base. Silurian graptolites from Silverdale near Bowning have recently been described (Sherrard and Keble, 1937, p. 306) as from the Lower Trilobite Bed^ of Mitchell. Detailed field mapping of the sediments in the Silurian Yass-Bowning syncline is at present being undertaken by Dr. Ida Brown, Mr. A. J. Shearsby and members of the Geology Department of the University of Sydney. The Rugosa from a small outcrop of Silurian beds along the western bank of the Murrumbidgee between the Boambolo crossing and the Taemas Bridge are also recorded, one * Sherrard and Keble have since considered (.in litteris) that these graptolites may have come from the sandstone at the top of the Great Shale, where Mitchell collected Orthis and Atrypa.