Qualitative and quantitative analyses of benthic foraminiferal faunas from the lower Mamu Formation of Leru in the southern Anambra Basin of Nigeria allow a detailed paleoecologic interpretation for the investigated section and the interpretation of depositional environments. The foraminiferal faunas represent marine to brackish deltaic deposits of prodelta to lagoon/interdistributary bay environments. Large parts of the fauna were described formerly as endemic from the Iullemmeden Basin. Their occurrence in the Anambra Basin indicates that, at least, an ephemeral marginal marine connection existed between the two basins during the Maastrichtian. Three of the reported species are new and are described here. These species are Ammotium leruensis sp. nov., Ammobaculoides parvus sp. nov., and Haplophragmoides pettersi sp. nov.