NORTH AMERICAN DIPTERA. 



TABLE OP GENERA. 



i. Flagelhim of antennae composed of numerous, more or less distinct 

 divisions; the antennae more or less elongated; five posterior 

 cells present in all cases. ....... 2 



Antennas short, or but little elongated, the third joint simple, with 

 a terminal or dorsal arista or terminal style; face small, usually 

 excavated; proboscis short; some or all the tibiae spurred (Lep- 

 ........... 8 



2. All the tibiae with spurs (Xylophagintz] . .... 3 

 Front tibiae without spurs (Arthroceratince} . ... 6 



XYLOPHAGIN^. 



3. All four posterior veins (i. e. the veins separating the posterior 



cells) arise from the discal cell; head small, scutellum with two 

 spinous protiiberances (Ccenomyintz) (fiig. 52, 3, 4). 



Ccenomyia. 



The last posterior vein arises from the second basal cell, the fifth 

 posterior cell hence not at all contiguous with the discal cell; 

 scutellum without spines. ....... 4 



4. Flagellum of antennae aciite at tip, eight-jointed; tibial spurs 1:2:2. 



Arthropeas. 

 Flagellum of antennae not acute at tip. ..... 5 



5. Fourth posterior cell closed; flagellum of antennae much elongated, 



composed of numerous (twenty-thirty) distinct divisions, often 

 pectinate; eyes emarginate near the antennae (20) (Rhnchice- 

 riiuf. ........ Rhachicerus. 



Fourth posterior cell open; flagellum composed of eight segments, 

 less distinctly separated and never pectinate (12, 13). 



Xylophagus. 



ARTHROCERATIN^:. 



6. Fourth posterior cell open, ....... 7 



Fourth posterior cell closed (17, and 7, 8 Stratiomyidez] . 



Xylomyia. 



7. Face projecting on each side in a rounded, subconical protuberance, 



thickly covered with hair (16) . . . . , Glutops. 



Face with two, deep, diverging fiirrows, running from base of an- 



tennae to oral margin (18, 19) , . Arthroceras. 



