Two new orthothecids from the Cambrian of the Barrandian area (Hyolitha, Skryje-Tyrovice Basin, Czech Republic)

Two orthothecid hyoliths Probactrotheca briketa new genus and new species and Circotheca smetanai new species are described from the Middle Cambrian Buchava Formation of the Skryje-Tyrovice Basin in the Czech Republic. The new forms are based on about twenty well-preserved external and internal moulds of opercula and conchs. The stratigraphic range and geographic distributions for both taxa are well known.