Cambrian trilobite Ovatoryctocara Tchernysheva, 1962 from Siberia

At present the species of the genus Ovatoryctocara Tchernysheva, 1962 are important stratigraphic markers of the boundaries between the traditional lower and middle Cambrian strata of Siberia.However, the vague taxonomic concept of the species and the lack of clear illustrations, which might demonstrate intraspecies variability, make the solution of the stratigraphic objective difficult.In regards to these problems, the genus has been revised on the basis of collections from east Siberian sections.Emended diagnoses for O. ovata (Tchernysheva, 1960), O. granulata (Tchernysheva, 1962), O. angusta (Tchernysheva, 1962), including subspecies O. angusta snegirevae (Suvorova, 1964), and O. doliiformis Korovnikov & Shabanov, 2008 are provided.In addition, the similarity between Siberian representatives of O. granulata and the specimens from South China and Greenland is established, based on meraspid morphology.Revision of the species shows that in the River Molodo section, O. granulata appears 20-25 cm higher than was previously documented.