A silicified Early Triassic marine assemblage from Svalbard Author Foster, William J. Jackson School of Geosciences, University of Texas, Austin, TX 78712, USA; & Earth Sciences, Plymouth University, Plymouth, PL 4 8 AA, UK; & Department of Earth Sciences, Natural History Museum, London, SW 7 5 BD, UK; Author Danise, Silvia Earth Sciences, Plymouth University, Plymouth, PL 4 8 AA, UK; & Department of Geology, University of Georgia, Athens, GA 30602, USA Author Twitchett, Richard J. Department of Earth Sciences, Natural History Museum, London, SW 7 5 BD, UK; text Journal of Systematic Palaeontology 2017 2016-11-10 15 10 851 877 http://dx.doi.org/10.1080/14772019.2016.1245680 journal article 10.1080/14772019.2016.1245680 1478-0941 10883052 3EBCAEF3-27C2-4216-9F18-89F195FA534F Genus Orbiculoidea d’Orbigny, 1847 Figure 2. A, Orbiculoidea winsnesi Gobbet, 1963 , NHMUK PI BE 3238, dorsal view, dorsal valve; B, Austrotindaria ? canalensis ( Catullo, 1846 ) , NHMUK PI MB 1198, external view, left valve; C–G, Promyalina schamarae ( Bittner, 1899 ) , external view; C, D, NHMUK PI MB 1204; C, right valve; D, left valve. E, F, NHMUK PI MB 1203; E, right valve; F, left valve. G, NHMUK PI MB 1202, right valve. Scale bars: A, B, G = 2 mm, C–F = 1 mm. Type species. Orbicula forbesii Davidson, 1848 ; Silurian , Wenlock ; West Midlands , England . Diagnosis. The generic diagnosis follows Mergl (2006) . Shell thin, strongly dorsibiconvex, subcircular, with subtrapezoidal outline of the posterior part. Ornament on both valves composed of regular raised concentric fila separated by broader interspaces. Dorsal valve is conical to subconical with subcentral apex; ventral valve with subcentral apex. Ventral valve depressed conical with subcentral apex. Pedicle track narrow, tapering posteriorly and anteriorly closed by shallow listrium; foramen in posterior end of listrium with short internal tube.