TABANUS FROM THE ANGLO-EGYPTIAN SUDAN. 177 latter, rather than a distinct species. While this is certainly possible, it seems for the present advisable—until the question can be definitely decided by the examination of further material belonging to both sexes—to concede specific rather than merely varietal rank to T. viordax. Although on a cursory examination Tahanus mordax may easily be mistaken for T. leucostomus, since, in the female sex at any rate, the abdominal markings in the two cases are identical, the former may be distinguished from the latter by the great development of the supra-antennal protuberance, and by the absence of an appendix to the anterior branch of the third lona-itudinal vein.