The present work is the result of the processing of Early and Middle Ordovician bivalves of the family Megalodontidae from the collections of O. N. Nikiforova (1951) and V. I. Dragunov (1957) in the basin of the Chuni River and S. A. Knyazev (1968). A. Knyazev (1968) in the Vilyui River basin.