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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. [ABSTRACT FROM AUTHOR]

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-Týlřovice 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. [ABSTRACT FROM AUTHOR]

The palaeographic distribution of hyoliths during the Ordovician is obviously not uniform. The main regions of hyolith appearance are European peri-Gondwana and African Gondwana. The diversity of hyoliths was increasing during the Ordovician with a peak in the Darriwilian (Llanvirnian; Oretanian) and highest peak during the Sandbian-Katian (Caradocian) interval. Hyoliths are highly endemic in all regions and all studied areas contain some possibly unique genera. This aspect is even more pronounced on the species level, because Gondwana, peri-Gondwana, Baltica and Laurentia share no species. [ABSTRACT FROM AUTHOR]