68 NORTH AMERICAN DIPTBRA. 



cut idled into a style or arista; {^composed of three simple joints 

 [sometimes apparently two), with or without a differentiated, one to 



three-jointed, style or arista. Second vein of the wing never furcate, 

 the third of/en; discal cell almost always present. 



14. Antennae composed of two or three simple joints, the distal one 



not annulated nor segmentated, usually with a one to three- 

 jointed terminal or dorsal arista or terminal style \d) , . 18 

 Antennae of the structure of (a) , (b),or(c). ... 15 



15. Empodia undeveloped or hristle-like; antennae elongate, the fla- 



gelluin composed of two or three joints, without apparent style; 

 front concave between the eyes in both sexes. ... 25 

 Empodia developed pulvilliform; flagelhun of antennae with nu- 

 merous, distinct joints, or forming the complex, so-called third 

 joint, with or without a differentiated style or bristle; body not 

 bristly. . 16 



B. Antenna composed of more than free joints, or the third-joint 

 complex, pour to eight segmented, inclusive of style or arista when 

 present: 



16. Squamae rather large; third longitudinal vein furcate; five poste- 



rior cells always present; the costal vein encompasses the wing; 

 tlagellum composed of from four to eight segments, never with 

 style or arista; males holoptic; proboscis of female adapted for 

 piercing. Horseflies, gadflies, greenheaded flies. 



Tabanidae, 176 



Squamae small or vestigial; for the most part flower flies; males 



usually holoptic. 17 



17. Tibiae without spurs; wing veins not crowded anteriorly: third 



antenna! joint composed of seven annuli with a terminal slender 

 style or arista: two submarginal, five posterior cells always pres- 

 ent, the fourth closed. Very large, robust, southern flies. 



Acanthomeridae, 173 



Tibia.* almost invariably without spurs: longitudinal veins of the 

 wings usually more or less crowded anteriorly, the posterior 

 ones often weak: the costal vein does not reach beyond the tip 

 of the wing; scutellum often with spines; third vein almost al- 

 ways furcate; four or five posterior cells, the fourth rarely or 

 never closed; antennae long or short (,!>), (c). 



Stratiomyidae, 104 



The middle tibiae, at least, with distinct spurs; the costal vein en- 



