The northwestern limit of the ecoregion is the Sanaga River, a faunal boundary for such species as the golden angwantibo (Arctocebus aureus), white-bellied duiker (Cephalophus leucogaster), mandrill (Mandrillus sphinx), and elegant needle-clawed galago (Euoticus elegantus).    From Wordnik.com.  [Northwestern Congolian lowland forests] Reference

For example, crowned guenon (Cercopithecus pogonias EN), moustached guenon (C. cephus), chimpanzee (Pan troglodytes, EN), agile mangabey (Cercocebus agilis), gray-cheeked mangabey (Lophocebus albigena albigenea), Guereza lowland colobus (Colobus guereza), potto (Perodicticus potto edwardsi), golden angwantibo (Arctcebus aureus), and western lowland gorilla occur only on the right bank of the Congo River.    From Wordnik.com.  [Western Congolian swamp forests] Reference