In this publication, the third of a projected series revising the Afrotropical (essentially southern African) species of the genus Quartinia Ed. André, 1884 (Hymenoptera: Vespidae: Masarinae), seventeen species are dealt with. Twelve new species from Namibia are described. They are: bella, clypeata, codoni, maculipennis, mandibulata, parva, pteroniae, pulawskii, setosa, tuberculifera, tuberculiventris and tuberculiventroides. With regard to five known species, albopicta (Richards), diana (Richards), minima Schulthess, poecila Schulthess and propinqua Schulthess, the descriptions of albopicta and diana are augmented by those of the hitherto unknown males, the descriptions of minima and poecila are corrected with reference to the type material and are augmented, in the case of minima, by an account of intra specific variation shown by a large sample from the seaboard of the Namib north of Swakopmund and, in the case of poecila, by an account of a remarkable geographic cline in colour pattern shown by specimens collected from localities ranging from Swakopmund (the type locality) in the north to Hondeklip Bay in the south. Extensive collecting data pertaining to all seventeen species contribute to the knowledge of their distribution and floral associations. An addendum to species described by Gess (2007) gives additional collecting data for Q. bonaespei, Q. conchicola and Q. vexillata.