1916.] NATURAL SCIENCES OF PHILADELPHIA. 511 
A Key to the Nearctic Species of Gonomyia. 
1. Two branches of the radial sector attain the wing-margin 
(Subgenus Leiponeiira Skuse.) 2 
Three branches of the radial sector attain the wing-margin 7 
2. Outer deflection of Mz absent, the cell 1st M-, being open 3 
Outer deflection of Ms present, the cell 1st M2 being closed 4 
S. Costa conspicuously china-white; legs banded with white; male 
hypopygium with the dorsal pleural appendage triangular, 
the caudal angle a prominent elongate spine; ventral pleural 
appendage a flattened blade whose inner caudal margin is 
armed with about five or six acute chitinized appressed teeth, 
of which the innermost is the largest. (Eastern United 
States.) alexanderi Johnson. 
Costa not conspicuously china- white; legs without white bands; 
male hypopygium with the dorsal pleural appendage broadly 
triangular, the caudal angle a short spine; ventral pleural 
appendage a flattened blade bearing near its dorsal inner side 
a sharp chitinized point; no serrations along the lobe. 
(Western United States.) cinerea Doane. 
4. Pleural stripes conspicuous; stigma distinct 5 
Pleural stripes indistinct or feebly indicated; stigma lacking or 
very faint 6 
5. Legs with the femora tipped with dark brown; costal margin of 
the wings conspicuously light yellow, the stigma pale brown. 
(Northeastern United States.) sacmidaga Alexander. 
Legs with the femora indistinctly darkened at the tip; costal 
margin of the wings not yellow, the stigma dark browoi. 
(Southeastern United States and southward.) 
pleuralis Williston. 
6. Pleura plumbeous with a pale yellow stripe; male hypopygium 
with the pleural appendage armed with a strongly curved 
hook. (Southeastern United States and southward.) 
puer Alexander. 
Pleura unstriped, pale; male hypop.ygium with the pleural 
appendage very elongate, slender, decussate in a position of 
rest, the inner face at the apex with a strong bristle. (Eastern 
United States.) manca Osten Sacken. 
7. Radial cross-vein present (subgenus Gonomyella Alexander) 
(Southeastern LTnited States and southward.) 
slossonce Alexander. 
Radial cross-vein lacking (subgenus Gonomyia Meigen) 8 
8. Basal deflection of Cui far before the fork of il/; subcosta long, 
ending beyond the origin of Rs 9 
Basal deflection of Cui at or beyond the fork of M; subcosta 
short, ending opposite or far before the origin of Rs 11 
9. Wings clear. (Northeastern United States.) 
mathesoni Alexander. 
Wings spotted • 10 
