Orbiculoidea d’Orbigny, 1847

Foster, William J., Danise, Silvia & Twitchett, Richard J., 2017, A silicified Early Triassic marine assemblage from Svalbard, Journal of Systematic Palaeontology 15 (10), pp. 851-877 : 854

Genus Orbiculoidea d’Orbigny, 1847

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.