OF WASHINGTON. 151 



presence and attack of the insects, it is convincing evidence, to 

 me at least, that a large percentage of the trouble heretofore 

 attributed to diseases, and other causes, may be brought about by 

 the attack of one or more species of so-called fungus-gnats. 



FIG. 9. Work of Epidapus scabiei* 



The species which I have found to be especially instrumental 

 in causing injuries and conditions which would be recognized as 

 the potato-scab blemish is a new and interesting Epidapus, for 

 the generic determination of which I am under obligations to Dr. 

 S. W. Williston. I take this occasion to present a full descrip 

 tion and figures of the species in its different stages of transfor 

 mation, under the specific name of Epidapus scabiei, and the 

 common name Potato-scab Gnat. 



In order to have better authority than my own limited knowl 

 edge of Diptera, I submitted the descriptions and drawings to 

 Dr. Williston, who has kindly revised the more important 

 descriptions, especially that referring to the wing.f 



* Observation 65263.. Tuber taken from barrel in cellar Nov. 18, 1893. 

 It had recently been attacked by larvae, which had apparently entered 

 through the stem. (Engraving from photograph, showing character of 

 tuber Jan. 25, 1894, at which time it would have been recognized by the 

 casual observer as ordinary potato-rot.) 



fl wish also to acknowledge, in this connection, the kindness of Mr. 

 L. O. Howard, Dr. J. A. Lintner, and Prof. S. A. Forbes, for extracts 

 from works not in our library, and for other special favors. 



