66 NORTH AMERICAN DIPTERA. 



Mesonotum never with a complete V-shaped suture, rarely with any 

 distinct suture. For the most part small or very small flies. 4 



4. A complete discal cell present; antennae twelve-sixteeu jointed; 



empodia developed pulvilliform, the pulvilli absent. 



Rhyphidae, 157. 

 No discal cell. 5 



5. Antennae composed apparently of two joints and a terminal arista, 



formed by nine or ten closely united segments; second basal 



cell present and small. Rare, small flies. Orphnephilidie, 153. 



Not such flies. 6 



6. Wings with only a few longitudinal veins and no apparent cross- 



veins, almost always hairy; antennae slender, usually twelve 

 to sixteen-jointed; coxae not elongate; tibiae without terminal 

 spurs; legs not thickened; ocelli present or absent. Small or 

 minute, delicate, mostly gall producing flies. 



Cecidomyidae, 117 

 Not such flies. 7 



7. Ocelli present* 12 



No ocelli. .......... 8 



8. The marginal vein is not continuous beyond the tip of th« wing. 9 

 The marginal vein encompasses the wing; second and fourth long- 

 itudinal veins furcate; many veined. .... 10 



9. Antennae slender; the joints more or less constricted, and often 



bushy plumose in the male; legs slender, the femora sometimes 

 thickened; abdomen slender, wings usually narrow; no sexual 

 holopticism. For the most part slender, delicate gnats; some 

 small forms blood-sucking ('punkies'.) Chironomidae, 1 10 

 Antennae alvvavs shorter than the thorax, composed of ten or 

 eleven closely united segments, and never plumose; legs strong, 

 the hind pair more or less dilated; body thick-set, the abdomen 

 ovate; anterior veins of wings stout, the posterior ones weak 

 (compare certain Bibionidae when in doubt as to the ocelli); 

 males holoptic. Small or minute, blood-sucking flies; black 

 flies, buffalo gnats, turkey gnats. . . Simuliidae, 144 



10. Wings ovate or pointed, with numerous longitudinal veins, and 

 without apparent cross-veins; veins very hairy: tibiae without 



* The presence or absence of ocelli is not a family character; a few 

 forms among both the Mycetophilnlae and Bibionidae appear to lack 

 them. 



