New data are given on biostratigraphy of the Lower Cambrian Oldynda Formation of the Ozerninsky ore cluster, Western Transbaikalia. The formation is subdivided into eight units; it dates from Atdabanian-Botomian, with the boundary running between stages along the base of the Nazarovo unit. It is concluded that the scheme of the stage subdivision of the Lower Cambrian of Siberia may be extrapolated to Transbaikalia. New species of archeocytes are described: Tumulocyathus postnikovi Zhur., Dupliporocyathus? terleevi Zhur.
