A REVISION OF THE NORTH AMERICAN TWO-WINGED 
FLIES OF THE FAMILY THEREVIDAE. 
By Frank R. Core, 
Of Stanford University, California. 
INTRODUCTION. 
This study of the Therevidae was a part of some graduate work 
done at Stanford University, beginning in the autumn of 1919. 
While at Washington, District of Columbia, a few years ago the writer 
made some notes on the types in the United States National Museum 
collection and named a personal collection of Therevidae by com- 
parison. It is to be regretted that no further reference to types 
(with a few exceptions) has been possible during the preparation of 
this paper. But most of the species are so well marked as to be easily 
identified from the descriptions, and authentically determined mate- 
rial from other dipterists has aided considerably. Possibly a few 
mistakes have been made due to not having seen all type material, 
but as there was no opportunity of doing this in the near future it 
seemed best to publish the results of this study at this time, rather 
than wait a number of years and delay progress on the work done 
in this family of diptera. 
Of the 82 previously described species the writer has examined 50 
during the progress of the work, 3 of this number being types. The 
32 species not available for study are largely uniques, and the types 
of a number are in Europe. The types of 9 of these rare species are 
in the United States National Museum, and the writer made notes on 
some of them when studying that material some years ago. Nine of 
the 32 species not examined are Mexican, but they may be taken in 
States along the border by future collectors. The writer collected 22 
species in addition to new forms, 15 of these in the type localities. 
Over 1,200 specimens were examined from various parts of North 
America, a collection extensive enough to give some idea of the species 
occurring in this region. 
The location of the types of new species is designated under the 
specific descriptions. The type material belonging to the writer has 
been placed in the United States National Museum, which also con- 
tains by original deposit or subsequent purchase nearly all of Kréber’s 
types. The names of the collectors are given in parentheses and the 
No. 2450.—PROCEEDINGS OF U. S. NATIONAL MUSEUM, VOL. 62, ART. 4. 
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