Revision of Sowerby’s species Spirifer bisulcatus, Spirifer pinguis and Spirifer rotundatus from the Visean of Great Britain

Sowerby's species 'Spirifer bisulcatus, Spirifer pinguis and Spirifer rotundatus' are here revised and their generic and suprageneric position assessed. The material on which the revision is based is housed at the Natural History Museum, London, and the provenance and history of the collections is also outlined. Spirifer bisulcatus Sowerby, 1825 is placed in the genus Angiospirifer Legrand-Blain based on its cancellate micrornamentation and occurrence of vascular markings. Spirifer pinguis Sowerby, 1821 and Spirifer rotundatus Sowerby, 1825 belong to Latibrachythyris n. gen. which is similar to Brachythyris M'Coy in its general shape, but differs in its wider hinge and presence of an apical median septum. Revision of the diagnosis of the superfamily Brachythyridoidea is thus required to include taxa with a wider hinge. During the Visean, the brachythyridoid families Brachythyridae and Skelidorygmidae show a tendency to increase the width of the hinge and to develop an apical septum or a myophragm.