232 The Ohio Naturalist. [Vol. V, No. 2, 



pilose eyes and ocelligerous tu1)ercle are put in Apatolestes, those 

 with pilose eyes and without the ocelligerous tubercle in Atvlotus 

 and the others with naked eyes and no ocelligerous tubercle form 

 the genus Tabanus. A large number of the species from the 

 region covered by this papar fall into Apatolestes and are the 

 hardest to characterize so others can recognize them. They 

 look much alike and it would seem sometimes that species are 

 made on meager characters, but a study of European species of 

 the genus convinces one that the older authors have done the 

 same thing, and moreover when one studies our own forms he 

 gradually comes to the same conclusion that the Europeans evi- 

 dently have, that is, it is practically impossible to characterize a 

 species at all when so manv points are considered as onlv varia- 

 tions of the same. 



It is my purpose that this paper supplement Osten Sacken's 

 Prodrome, therefore some of the species that occur almost as far 

 west as the Rocky Mountains may not be considered while some 

 that are rightly eastern species are included because they are not 

 treated by Osten Sacken. 



The following key is offered as an aid for separating a most 

 difficult group: 



1. Eyes naked 2 

 Eyes pilose 13 



2. Large species, abdomen uniformly black or brown 3 

 Smaller species, abdomen bicolored 6 



3. Wings with a dark spot at the fvircation of the third vein 4 

 Wing without dark coloration at the furcation of the third vein 5 



4. Thorax covered with white pollen or down piinctifer 

 Thorax brown with narrow white stripes benedictus 



5. Wings black atratus 

 Wings subh valine ccgrotus 



C). Wings with large brown patches venustus 



Wings hyaline 7 



7. Abdomen brown with white posterior mai\gin to each seg- 



ment aytnulatiis 



Abdomen not so marked S 



8. Abdomen with a uniform white stripe from the scutellum to the 

 end of the abdomen liiicola 

 Abdominal markings not in the form of a uniform band 9 



9. Abdomen with a middorsal row of unconnected white triangles 11 

 Abdomen not so marked, small species, not more than 12 



millimeters in length 10 



10. Abdomen gray, with four small l)lack spots on each of segments 



two to six cribcllmii 



AljdoiTien with three irregular gray stripes composed of con- 

 i tiguovTS spots, base of anterior branch of the third win witli 



a long oblique stump productus 



Abdomen black with a very narrow wliitc border to each seg- 

 iTient, and on either side a row of very small white sjiots jratcllns 



11. General color of abdomen l)rown ftavidits 

 General ctilor (.)f alxlomen black 12 



