Gracilitheca astronauta n. sp. and Nephrotheca sophia n. sp. (Hyolitha, Orthothecida) from the Cambrian of Czech Republic

Two orthothecid hyoliths, Gracilitheca astronauta n. sp. and Nephrotheca sophia n. sp. are described from the “middle” Cambrian Buchava Formation of the Skryje-Týřovice Basin in the Czech Republic. The new forms are based on about thirty well-preserved external and internal moulds of both conchs and opercula. Gracilitheca astronauta n. sp. is classified under the family Gracilithecidae Sysoev, 1972 and may be distinguished by clearly triangular cross-section of the conch, whereas Nephrotheca sophia n. sp. is characterized by transversally elongated cardinal processes reaching the lateral opercular margin and is combined with the family Orthothecidae Sysoev, 1958 emended Malinky, 2009. Several specimens of G. astronauta show operculum preserved inside of the conch. Stratigraphic ranges and geographic distributions within the Skryje-Týřovice Basin are established for both taxa.