The writer's original intention in publishing this paper was to give a key for the identification of those African mosquitos which might be taken by the nonspecialist for species of Culex, without attempting to form any opinions as to the value or limits of allied genera. A study of the insects, however, led to the realisation that scale characters, in this group at least, are not of very great value for separating genera, and consequently the present paper gives the author's views of the classification of the Culex group, and is more complete than it might otherwise have been. Time has not yet been available to deal with those species which have flat scales on the top of the head or on the scutellum (Stegomyia group).