274 NORTH AMERICAN DIPTERA. 



of diptera. * Many of the species have the wings- prettily 

 marked. The family by some entomologists is divided 

 into several independent groups, as the Doryeeridae or 

 Pyrgotidae, the Platystomidae, Ulidiidae, etc. The flies 

 are usually found about meadows or among luxuriantly 

 growing grass. The larvae are but poorly known. 



TABLE OF GENERA. 



BY PROF. W. A. SNOW, REVISED. 



1. Eirst longitudinal vein beset with small bristles. ... 2 

 First longitudinal vein bare 5 



2. Ovipositor flattened; ocelli present. ..... 3 



Ovipositor not flattened; no ocelli Pyrgotinae. 



3. Third antennal joint round or short ovate; ends of auxiliary and 



first longitudinal veins widely separated. . Pterocallinae. 

 Third antennal joint not round or short ovate.* ... 4 



4. Neither pro-pleural nor nieso-pleural bristles present; third anten- 



nal joint elongate Platystominas. 



A nieso-pleural but no pro-pleural bristle present, Cephalinae. 

 Both a nieso-pleural and a pro-pleural bristle present. Ortalinse. 



5. Posterior angle of anal cell drawn out into a lobe, or at least, more 



or less acute; femora never armed. . . . TJlidinae. 



Posterior angle of anal cell obtuse; rounded or retracted; femora 



armed in most of ths genera. . . . Richardiinas . 



PYRGOTIN^. 



Front strongly projecting; face retreating; oral opening small; pro- 

 boscis not incrassated; clypeus but little developed; ocelli absent; no 

 pro-plenral bristle; first longitudinal vein hairy; ovipositor not flat- 

 tened (1) ' . Pyrgota. 



PI.ATYSTOMIN^, 

 Oral opening very large; clypeus generally very much developed, 

 and the proboscis proportionately stout; third antennal joint elongate; 

 mesonotum bristly on the hind part only; pro-pleural and nieso-pleu- 

 ral bristles absent; female abdomen with five segments; ovipositor 

 flattened; first longitudinal vein bristly. 



* TetropismetlUS Loew has the third antennal joint circular, but its 

 short stigma or subcostal cell locates it among the Ortalinae. 



