The Ohio Naturalist 
[Vol. V, No. 2, 
23 
2 
pilose eyes and ocelligerous tubercle are put in Apatolestes, those 
with pilose eyes and without the ocelligerous tubercle in Atylotus 
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 many points are considered as only 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 vSacken. 
The following key is offered as an aid for se])arating a most 
difficult group: 
1 . Eyes' naked 2 
Eyes pilose 12 
2. Large species, abdomen uniformly black or brown .3 
Smaller species, abdomen bicolorcd G 
8. tVings with a dark spot at the furcation 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 punctifer 
Thorax brown with narrow white stripes benedict ns 
5. Wings black atratns 
Wings subhyaline ceerotns 
G. Wings with large brown patches venustns 
Wings hyaline 7 
7 Abdomen brorvn with white po.sterior margin to each seg- 
ment annulatns 
Abdomen not so marked 8 
8. Abdomen with a uniform white stripe from the scutellum to the 
end of the abdomen lineola 
Abdominal markings not in the form of a uniform band 9 
9. Abdomen with a middorsal row of unconnected white triangles 1 1 
Abdomen not so marked, small species, not more than 12 
millimeters in length 10 
10. Abdomen gray, with four small black spots on each of segnients 
two to six ' cribellnm 
Abdomen with three irregular gray stripes composed of con- 
tiguous spots, base of anterior branch of the third vein with 
a long obliciue stump prodnetns 
Abdomen black with a very narrow white border to each seg- 
ment, and on either side a row of very small white spots jratellus 
11. General color of abdomen brown flavidiis 
General color of abdomen black 12 
