!6 2 NORTH AMERICAN DIPTERA. 



TABLE OF GENERA. 



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

 divisions; the antennae more or less elongated; five posterior 

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



Antennae short, or hut 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 \J.rp- 

 i i ii(f). 8 



2. All the tibiae with spurs [Xylophaj^incs). .... 3 

 Front tibiae without spurs {Arthroceratincz) . ... 6 



XYLOPHAGINiE. 



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



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

 Spinous protuberances (< 'iriioiiiyin(f) (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 acute at tip, eight-jointed; tibial spurs 1:2:2. 



Arthropeas. 

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



5. Fourth ]x)sterior cell closed; flagellum of antennae much elongated, 



composed of numerous (twenty thirty 1 distinct divisions, oiten 

 pectinate; eyes emarginate near the antennae (23) 1 Rhachice- 



rince Rhachicerus. 



Fourth posterior cell open; flagellum composed of eight segments, 

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



Xylophagus. 



ARTHROCERATINJg. 



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



Fourth posterior cell closed (17, and 7, 8 Stratiomyid.ee) . 



Xylomyia. 



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



thickly covered with hair (16) Glutops. 



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

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



