W.H. Turton (1932: 252) described Donacilla africana as a new species from Port Alfred, South Africa. However, judged by the characters of the hinge, the principal points of distinction between the genera in the Mesodesmatidae, this species belongs to the genus Mesodesma Deshayes, 1832. The pallial line, however, differs so much from that of the other species in this genus, that it is impossible to classify it with one of the known subgenera. I therefore want to erect a new subgenus for which I designate Mesodesma africanum the type-species. I propose the name Regterenia in dedication to Dr. C.O. van Regteren Altena on the occasion of his 65th birthday.