100 NORTH AMERICAN DIPTERA. 



1'). Femora thickened ; hind tibice usually much dilated and with tubercles 

 on outer side ; basal cells large ; first posterior cell narrowed ; all 

 the tibiaj with preapical bristle. . . . Riiopalomeuidk. / 2 y 



Flies without the above characters l(> 



10. Front bristly on the sides and at the vertex. .... 17 

 Front bristly at the vertex only ; the auxiliary vein is not steeply in- 

 clined where it joins the costa. ...... 20 



17. Hind tibia?, at least, with a preapical bristle. .... 18 

 Hind tibiae without preapical bristle. ...... 10 



18. Basal cells of wings small SAPRoMTzmiE.y 2.3 



Basal cells of wings of moderate size and distinct. . Sciomyzid.ic. /"i,"! 



10. Posterior basal cells of wings small, the anal cell never produced 

 acutely; a single bristle on each side of the front (Lonc/Hcina). 



Sapkomvzid.e. J 9-3 

 Posterior basal cells of wings of moderate size, the third (anal) often 

 produced into an acute point Trypetid/B. H Y 



20. Legs elongate, often very long; alKlomeii narrow and long, often nmch 



narrowed at the base. ........ 21 



Legs not elongated; abdomen comparatively short, or, if long, not nar- 

 rowed at the base Ortalid.k. //'y 



21. First posterior cell narrowed in the margin or closed. Micropezid.k. | I 3 

 First posterior cell not narrowed in tlie margin, or but slightly so;* 



palpi rudimentary or wanting Sepsid.ic. // / 



22. Eyes inserted at the tip of lateral processes. . . . ])i<)p.sin.K. //y^ 

 Head not prolonged into lateral processes 2.j 



23. Hind metatarsi shorter than the following joint, incrassate. Borborid.e. / p / 

 Hind metatarsi longer than the following joint, not incrassate. . 24 



24. Discal and second basal cells united, the separating cross-vein rudimen- 



tary or wanting ; posterior cross-vein present.! . . . 25 

 Discal cell se])arated from the second basal cell by a distinct cross- 

 vein, or, if not, the posterior cross-vein also wanting. . . 20 



25. Legs long and slender ; abdomen elongate and narrow. Micuopezid.e. //^ 

 Legs of moderate length, often strong; abdomen ovate or elongate 



elliptical. ........... 2() 



20. Front bare, or, at the most, bristly at the vertex; third antennal joint 



rounded, or, if elongate, the head triangular in profile. OsciNin.-K. f Q^ 

 Front bristly at least as far as the middle ; head never triangular in 

 profile - .... 27 



* Compare here the Psilidw. when there is doubt regarding the auxiliary 

 vein. t 1'he posterior cross-vein is wanting in Asteia {iJrosojihi/iiht), 



EllipoiK'urd {Oxciniflii), I^/ii/tiinii/za {Ai/r(»iii/zl(l<i). 



