In preparing his first synopsis of the African species of Culex (Bull. Ent. Res., ii, pt. 3, Oct. 1911) the writer relied almost entirely upon characters of coloration for the separation of species, and had made no study of the male genital organs; at the same time it was pointed out that the group of species allied to Culex invidiosus required much additional study before their classification could be regarded as satisfactory. It is now possible to give in full the results of further study of the African species of Culex of the pipiens and invidiosus groups. It has been found that, in these groups at least, the species can most readily be separated by means of the male genitalia, and also that one or two names which had previously been sunk as synonyms must in reality stand as good species. In the present contribution figures are given of the male genital organs of eleven species; these, together with the four already illustrated (Bull. Ent. Res., iv, pt. 1, May 1913) comprise all the African Culex with the exception of (1) those with a banded proboscis; (2) those with characteristic leg markings, C. tigripes and C. tipuliformis; (3) C. pruina, which is described below; (4) C. didieri, N.L., and C. pygmaeus, N.L., which the writer is unable to recognise; and (5) those with the pale markings of the abdomen situated towards the apices of the segments. As before, all the figures have been prepared by Mr. A. J. Engel Terzi with very great care and accuracy, and I am much indebted to him for his assistance in this difficult piece of work.