The limits of the subgenus Atylotus as restricted by Osten–Sacken are not easy to determine. The presence or absence of the ocelligerous tubercle is the character which gives most trouble, for in some species it seems to be absent in the female and present in the male, and one could convince himself without a great amount of imagination that in some species it is present in one specimen and absent in another of the same sex. the type of the subgenus is bicolor, and associated with it are other equally peculiar species whose characters place them at once in Atylotus. They are small forms in which the usual banding of the eyes is lacking, as are also the frontal callosity and subcallous. The wings are glassy, transparent, resembling those of some other Tabanids when teneral.