Mastacembelus liberiensis Boulenger, 1898 of West Africa is discussed with reference to its distribution within the Konkoure River basin (Guinea). The synonymies of M. reticulatus Boulenger, 1911 and M. laticauda Ahl, 1937 with M. liberiensis are both confirmed. Further, intraspecific meristic, morphometric and colour pattern variation within M. liberiensis is documented and discussed. Finally, a new species, M. kakrimensis sp. nov., endemic to the Konkoure River basin is identified and described. (c) 2005 The Fisheries Society of the British Isles.