PROCEEDINGS OF THE Entomological Society of Washington Vol. 76 MARCH 1974 No. 1 UNDESCRIBED HORSE FLIES FROM THE SOUTHWESTERN UNITED STATES AND NORTHERN MEXICO (DIPTERA: TABANIDAE) John F. Burger 12116 Gaynor Road, Rockville, Maryland 20853 ABSTRACT — From a study of the biology and taxonomy of Arizona Taba-nidae, 2 new species in the Tabanus gilanus group and the male of Tabanus boharti Philip are here described and illustrated for the first time, notes on larval habitats are presented, and a key is given to differentiate the adults of most species in the Tabanus gilanus group occurring in Arizona. While studying the biology and taxonomy of immature Tabanidae in Arizona during 1968-1970, I collected and reared 2 previously undescribed species of Tabanus and the undescribed male of Tabanus boJiarti Philip. These species are allied with the Tabanus gilanus group of horse flies. Tabanus boharti Philip fig. 1 Neallotype $ , 15.0 mm. Eyes sparsely pilose, hairs short; eye pattern in life 2 very narrow light green bands on brownish-purple ground; areas of large and small facets sharply differentiated, upper % of eye with large facets. Frontal triangle grayish pollinose, with yellowish tinge along margin of eye and irregular black spot at apex above. Face and genae whitish pollinose, except yellowish tinge along margin of eye. Anteimae dark brown basally, black beyond dorsal angle of plate; first segment robust but not extended above second segment dorsally; plate of tliird segment about 1.2 times longer than broad, dorsal angle prominent, excision shallow; annulae about as long as plate. Palpi yellowish, covered witii grayish pollen and white hair; second segment stout, with small, downward-pointing nipple; length of second segment about twice width. Thorax with gray and black lines distinct; dorsal surface densely covered with erect white and black hair, white hair predominant, and clothed with mixture of black and cupreous appressed hair; scutellum concolorous with thorax. Pleura and coxae whitish pruinose, densely clothed with white hair. Legs dark, covered with gray pollen; basal V2 of fore-tibiae and basal % of mid-and hind-tibiae yellowish orange, remainder black; tarsi black. Wings hyaline, veins dark brown.