66 Proceedings of the Biological Society of Washington. 



Key to Genera and Species. 



1. Upper pair of cephalic processes thorn-like, widely separated at 



bases; lateral cephalic process or processes long;, thorn-like ... 2 



— Upper pair of cephalic processes stout, not thorn-like, contiguous 



for the greater portion of their length ; lateral cephalic process 

 small, tubercle-like 7 



2. Antero-lateral margin of head with a single long thorn 3 



— Antero-lateral margin of head with 2 long thorns, the bases of which 



are contiguous 4 



3. The transverse series of short thorns on abdominal segments 2-4 



with their bases and apices turned up at right angles ; labrum 

 unarmed * Spogostylum anale. 



— The short thorns in transverse series on segments 2-4 turned up at 



apices only ; labrum with a bifid thorn near apex 



Chrysanthrax fulvohirta. 



4. The short, stout thorns on abdominal segments turned up at bases 



and apices Exoprosopa fasciata? 



— The short, stout thorns on abdominal segments turned up at apices 



only 5 



5. Transverse armature of first abdominal dorsal segment consisting of 



a series of short, stout thorns on middle portion, and a number 



of long, slender, closely placed hairs on each side 



Exoprosopa fascipennis. 



— Transverse armature of first abdominal dorsal segment consisting of 



a few widely placed hairs, the middle portion either entirely bare 

 or with very slight indications of small tubercles which do not 

 appear as distinct thorns 6 



6. Lower one of the pair of lateral cephalic thorns simple apically, but 



with a small wart-like protuberance at base on lower surface, the 

 small wart bearing 2 distinct hairs; wings without discal pro- 

 tuberances Sparnopolius fulvus . 



— Lower one of the pair of lateral cephalic thorns with a short sub- 



apical protuberance, the apex of thorn turned upward, base 

 simple; wings each with a pair of protuberances, one about one- 

 fourth from base and the other near middle . Anastoechus nilidulus. 



7. Eighth ventral abdominal segment without hairs on disc 



Hyalanthrax hypomelas. 



— Eighth ventral abdominal segment with hairs on disc 8 



8. Eighth ventral abdominal segment with 2 hairs on each side of disc; 



distance from the pair of thorns on lower central portion of head 

 to apex of basal portion of sheath of mouth parts about 4 times 

 as great as distance from the latter to apex of proboscis .... 



Hyalanthrax lateralis. 



— Eighth ventral abdominal segment with 10-12 long hairs on disc; 



distance from the pair of thorns on lower central portion of head 



to apex of basal portion of sheath of mouth parts about twice as 



great as distance from the latter to apex of proboscis 



Hyalanthrax alternata. 



•This genus name has been emended to Spongostylum by some European authors. 

 (See Verrall. " British Flies." Vol. 5, 1909, p. 517.) 



