Shells of two species of freshwater bivalve (Unio willcocksi Bullen Newton and Etheria elliptica Lamarck) from the predynastic Gerzean (Nagada II) Decorated Tomb at Hierakonpolis, Egypt have given dates of 5000 ± 90 BP for the tomb, and 12,900 ± 120 BP for an episode of Nile terrace accumulation (correlated here with the Sahaba-Darau aggradation event). The archaeological and geological significance of these results is discussed, together with an outline of problems associated with radiocarbon dating of shell. Comparisons are made with the few other radiocarbon dates available for the Predynastic period in Egypt; possible reasons for the presence of shells in the tomb are considered.