Syrphidae of Nebraska 15 



and gently arched, never produced forward at oral margin and 

 entirely clothed with pile; a stigmatical cross-vein present; 



third vein usually (absent only in Mixogaster) with an adventi- 

 tious and free branch projecting into the first posterior cell 



(discal cell, Shannon) ; apical cross-vein upright or recurrent; 

 both sexes with three to four visible abdominal segments exclu- 

 sive of genitalia; males dichoptic Microdontinue 



Antennae not elongate and possessing dorsal arista, excepting 

 in a few genera, which are without a stigmatical cross-vein, 

 and the apical cross-vein is parallel with the wing margin 

 (Chrysotoxiim and Sphecomyia) ; or, if the apical cross-vein 

 is upright or recurrent (Chrysngaster) , then the mouth is pro- 

 duced forward 4 



4. The humeral calli and region between them distinctly destitute of 

 pile, the head being "cupped" over the anterior end of thorax, 

 causing the pile to end abruptly behind the posterior margin of 

 humeral region (the head may have to be removed to permit 

 examination) ; antennae placed well above middle of head; 

 arista usually a little shorter than length of antennae; abdo- 

 men of both sexes with five visible segments exclusive of geni- 

 talia; anterior cross- vein placed well before middle of discal 

 cell Syrphinae 



Pile extending upon the humeral region, abdomen of males with 

 only four visible segments exclusive of hypopygium, females 

 with five 5 



5. Apical cross-vein recurrent at distal end; marginal cell closed; 

 arista with either long or very dense plumosity; face protrud- 

 ing downwards; wings broad; alula very broad; squamae 

 usually very broad; thorax frequently bearing bristles. .yoZ»ce//i7iae 



Apical cross-vein parallel with wing margin, or, if recurrent 

 {Chry so g aster, Eumerus and Merodon) , the arista is bare 6 



■6. Arista long plumose for at least the greater two-thirds of its 

 length; marginal cell open; anterior cross-vein placed near or 

 beyond middle of discal cell; either yellow markings present on 

 abdomen, or with dense pile more or less yellow, except Pyritis, 

 which has long dense brownish pile; face protruding downwards, 

 or swollen, or tuberculate; the right prong (or style, Metcalf), 

 of the forceps of the genitalia is longer than the left one and 

 tapers to a sharp point, the left prong developed as an obtuse 

 lobe Sericomyinae 



121 



