The variation of A. mauritianus was discussed long ago by Alcock (Jl. Lond. Sch. Trop. Med., i, pp. 89–93, 1912), who concluded that the differences observed were due to mere individual variation. In my key to African Anopheles (Bull. Ent. Res., iii, p. 250, 1912) I suggested that an East and a West African form might be distinguished by the amount of white on the hind tibia and first tarsal segment. Careful study of more extensive material has shown that this generalisation cannot be maintained, but that there are four varieties of the species which can be rather easily distinguished, and fortunately the published names can be applied to them. Diagnoses of these varieties have been given by Miss A. M. Evans in her recently published guide to the African Anophelines (Memoir No. 3, New Series, Liverpool Sch. Trop. Med., Oct. 1927), but the definitions are somewhat expanded in the notes below, and a further account of the distribution is given. The variations are certainly of more than individual significance, because they show a distinct tendency to localisation, and bred series from one place do not exhibit much variation. On the other hand, I do not consider that there is more than one species, because no differences are apparent in the male hypopygium; I have mounted specimens of each of the four varieties and find them all to agree rather closely with Christophers' description and figure. In one point, however, Christophers' account seems to be at fault: the mesosome has always two or three pairs of distinct leaflets, the longest of which are nearly one-third as long as the tube.