38 DIPTERA OF NORTH AMERICA. 



ture of the face, the character of the family would have then to be 

 slightly altered. Mr. Walker has described a N. A. species which 

 he contends to belong to ACTORA. 



FAM. XLI. PSILIDAE. 



Charact. Body elongated, with sliort hairs and almost without bristles. 

 Neuration of the wings complete ; the axixiliary vein lies close by 

 the first longitudinal vein, but diverges from it at its end and runs 

 towards the border of the wing ; by a transverse fold most charac- 

 teristic in this family running from the tip of the auxiliary vein as 

 far as the base of the third posterior cell, the outward end of the 

 auxiliary vein is obliterated ; the posterior basal cells are very 

 large. Front with only a few bristles in the neighborhood of the 

 crown ; face receding ; opening of the mouth small and with no 

 bristles at its border. Only the middle tibiae have spurs, and all 

 the tibiae are without erect bristle on the outside. 



This family is represented in N. A. by the genera LOXOCERA, 

 PSILA, and CHYLIZA. The N. A. species, which induced Mr. 

 Walker to form a new genus Prochyliza, placed by him close by 

 Chyliza, belongs to some other family. 



FAM. XLII. MICROPEZIDAE. 



Charact. Body slender, elongated, with very short hairs and very scarce 

 bristles. Legs proportionately short ; only the middle tibiae have 

 spurs, these being generally very small and weak ; no small erect 

 bristle on the exterior side of the tibiae. Neuration of the wings 

 complete ; first longitudinal vein bare ; the auxiliary vein is very 

 close by it and diverges from it towards its end only ; the two 

 posterior basal cells are very large. Front with some bristles in the 

 neighborhood of the crown only; bordering of the mouth without 

 vibrissse. Last segment of the abdomen of the female prolonged 

 into a blunt, cylindrical tube. 



The family Micropezidse comprises genera which differ among 

 each other, both in the form of the head and the structure of the 

 antennae and oral parts. The head is sometimes rounded, some- 

 times more elongated ; the bristle of the antennae is generally dorsal, 

 but in some genera apical ; the clypeus sometimes very much de- 

 veloped, sometimes only rudimentary; the palpi sometimes large, 

 sometimes small, but never rudimentary. The clypeus being very 

 much developed and the proboscis very much thickened in the 



