Two new species of Marconia are described – Marconia mzinga and M. kizinga. Both species were collected from the same locality in the Uluguru North Forest Reserve, Morogoro District, Tanzania, in sub-montane forest habitat at an altitude of 1250–1500 m asl. The shells of the two species are morphologically very similar but they differ consistently in size without intermediates. Data on the genital anatomy and radula of M. mzinga are presented. Options for the generic status of the species and their possible relationships within the Streptaxidae are discussed.