2 NORTH AMEEICAN DIPTERA. 



3. Dorsum of thorax with a complete. V-shaped suture ;* wings (wanting 



rarely) many-veined, often with a complete discal cell; ocelli want- 

 ing (present in a few forms); often large flies. . . TIPULIIXE. 

 Dorsum of thorax without a V-shaped suture, or rarely with any 

 transverse suture : . . . 4 



4. A complete discal cell present; empodia developed pulvilliform, the 



pulvilli rudimentary. RHYPHID^;. 



No discal cell. . 5 



5. Antennae composed apparently of three joints with a terminal arista; 



small species, three or four millimeters in length. ORPHNEPHILID^E. 



Antennas not apparently composed of three joints and a terminal 



arista. . . . . w . . - 6 



6. Wings with only a few longitudinal veins, and no cross-veins ; coxae not 



elongate, tibiae without terminal spurs, legs not thickened ; ocelli 

 present or absent; smaller minute, delicate, mostly gall-producing 



flies. CECIDOMYID^E. 



Not such flies ; wings usually many- veined. .... 7 



7. Ocelli present 8 



Ocelli wanting (compare Mycetophilidce) 10 



8. Wings broad, bare, characteristically marked by numerous folds be- 



tween the veins, giving a netted, spiderweb-like appearance. 



LlPONEURIDJE. 



Wings not so marked ; no entire transverse suture. ... 9 



9. Coxae much elongated (moderately so in Sciarince); antennae often elon- 



gate, the joints constricted ; three or two ocelli present (in the latter 

 case one situated near each eye and often perceptible with difficulty); 



all the tibiae with spurs MYCETOPHILIDCE. 



Coxae short, the thorax rounded, not humped above ; antennae shorter 

 than the thorax, thickened, the joints closely united without marked 

 constrictions ; legs strong, the front femora often thickened ; empodia 

 pulvilliform, the pulvilli sometimes absent ; eyes of 5 large. 



BIBIONIDJE. 



10. The costal or marginal vein does not extend beyond the tip of the 



wing. . . . 11 



The marginal vein encompasses the entire wing. ... 12 



11. Antennae slender, the joints more or less constricted, and often bushy 



plumose; legs slender, hind tibiae and metatarsi never dilated; abdo- 

 men slender; wings narrow. . . . . CHIRONOMID^E. 



* Bittacomorpha, Ptychoptera and Idioplasta may cause doubt here. They 

 have the suture incompletely V-shaped and sinuous. Compare Rhyphidce. 



