32 DIPTERA OF NORTH AMERICA. 



order to retain the accustomed arrangement as much as possible, 

 I shall leave them in their usual places, though it would seem, that 

 a more natural arrangement might be obtained, were they added 

 to the above families which have the basal cells prolonged. 



Pam. XXXI. DOLICHOPODIDAE. 



Charact. — First basal cell rather short, the second united with the discal 

 cell, the third small ; auxiliary vein running in the first longitudi- 

 nal vein ; third longitudinal vein simple, the fourth sometimes fur- 

 cate ; no intercalary vein. Hypopygium symmetrical, bent under 

 the abdomen. Empodium small, membranaceous, of a linear form. 



The principal genera are: Psilopus Meig., Sybistroma Meig , 

 Hypophyllus Hal, Hercostomus Loeiv, Hygroceleutiius Loew, 

 Polichopus Meig., Tachytreciius Stann., Orthochile Lair., Gym- 

 nopternus Loew, Lyroneurus Loew, Plagioneurus Loew, Lian- 

 calus Hal., Scellus Loew, Hydropiiorus Fall, Campsicnemus 

 Hal, Thinophilus Wahlb., Peodes Loew, Achalcus Hal, Sys- 

 tenus Loew, Syntormon Loew, Synarthrus Loew, Porphyrops 

 Meig., Rhaphium Meig., Xiphandrium Hal, IIaltericerus 

 Bond., Smiliotus Loew (= Machserium Hal.), Argyra Macq., 

 Leucostola Hal, Xematoproctus Loew, Saucropus Loew, Xan- 

 thochlorus Loew, Sympycnus Loew, Teuchophorus Loew, Anep- 

 sius Loew, Eutarsus Hal, Diaphorus Meig., Chrysotus Meig., 

 Chrysotimus Hal, Medeterus Fisch., Aphrosylus Hal. 



The X. A. genera which I am acquainted with are : Psilopus 

 Meig., Hygroceleutiius Loew, Dolichopus Meig., Tachytrechus 

 Stann., Gymnopternus Loew, Plagioneurus Loew, Liancalus 

 Hal, Scellus Jjoew, Campsicnemus Hal, Synarthrus Loew, 

 Porphyrops Meig., Argyra Macq., Leucostola Hal, Saucropus 

 Jjoew, Xantiiochlorus Loeiv, Diaphorus Meig., Lyroneurus 

 Loew, Chrysotus Meig., and Medeterus Fisch. 



Fam. xxxii. oestridae. 



Charact. — Antenna; inserted in rounded pits ; the middle part of the fare 

 exceedingly narrow ; the opening of the mouth very small ; the oral 

 organs rudimentary. Teguhe large. 



This family has often been considered as very distant from the fol- 

 lowing, but the late discoveries have brought to light forms which 



