Silurian athyridide brachiopods from Yass, New South Wales

ATHRYIDIDE brachiopods were included amongst the fossils listed in early papers describing the geology and stratigraphy of the Yass -Bowning area (Jenkins 1879;Mitchell 1887;Shearsby 1912;Sherrard 1936;Brown 1941).Mitchell (1921) described Molongia elegans (based on and illustrated by specimens from Molong, NSW) and Retzia salteri (illustrated by one poor specimen from the Hume Limestone Member).Neither of these can be recognised in the material I have studied, including Mitchell's collections now held by the Australian Museum.In the present paper I describe three other athyridide taxa from Yass, of which two are new.In addition, a lectotype for M. elegans (genotype) is chosen, briefly described, and illustrated.Unsurprisingly, Nucleospira paula n. sp. is found over an extended stratigraphic range (for an account of the Yass succession see Strusz 2002).At Yass it is known from the Barrandella Shale to the lower Cowridge Siltstone, and at nearby Canberra the same species has been reported (in smaller numbers) from the late?Wenlock Walker Volcanics (the age is uncertain, but on stratigraphic grounds is older than the Yass Formation), and is probably also present in the Yarralumla Formation (a lateral equivalent of the Yass Formation).This gives a total range of late?Wenlock to Přídolí.The diminutive Navispira?bicarinata n. sp. has nearly the same stratigraphic range -Yass Formation or basal Silverdale Formation to lower Cowridge Siltstone.Finally, a few specimens of Coelospira cavata Strusz, 1982, are described from the Yass Formation, the basal Black Bog Shale and possibly the Barrandella Shale.The distribution of these few taxa is shown in Figure 1.Strusz (2002) gave an account of the sources of material used in revising the Yass faunas, including an assessment of their reliability.Details of the localities, including possible Benthic Community assignments for each, were given in the Locality Appendix of Strusz (2002), with additions by Strusz (2003Strusz ( , 2005)). MATERIAL AND LOCALITIES SYSTEMATIC PALAEONTOLOGY Classification.The classification used here is that given by Alvarez & Copper (2002). Measurements and symbols.All linear measurements are in millimetres, and unless otherwise specified are as defined by Williams & Brunton (1997); the following symbols are used for these measurements: Ls, Ws -maximum shell length, width.Wh -hinge width.Lv, Ld -ventral valve length (usually coincident with Ls), dorsal valve length.Ts, Tv, Td -thickness of shell, ventral valve, dorsal valve.L(Wmax) -length to widest part of shell.Repositories.The repositories for the specimens studied are shown by the following prefixes to their catalogue numbers: AMF, macrofossil collection, Australian Museum, Sydney; ANU, Department of Earth & Marine Sciences, Australian National STRUSZ, D.L.,