66 Key to Families of North American Insects. 



(Hybos, Hemerodromia, Clinocera, Platypalpus, Rhamphomyia) (PI. 11, 

 fig. ^251; PI. VI, figs. 268, 270, 300.) 



(EMPID^, mduding HV BO T I D.E) EMPIDID^ 

 Basal cells small and indistinct, discal cell merged with the second basal cell, 

 third vein never forked; calypteres rather large and fringed; proboscis almost 

 always fleshy; abdomen typically with five or six segments excluding the 

 large inflexed genitalia of male; usually metallic green. (Sciapus, 

 Dolichopus, Gymnoptemus, Chrysotus, Hydrophorus.) (PI. 12, figs. 274, / 

 299) DOLICHOPODID^ ^ 



35. Anal cell elongate, acute, usually closed toward the wing-margin, but at least 



longer than the second basal cell which is generally long; frontal suture 



rarely distinct. (Aschiza, Athericera) 36 



Anal cell, if present, short, closed far from the wing-margin, not acutely pro- 

 duced except rarely by a lobiform prolongation, second basal cell much 

 shorter than the third posterior cell except in the abnormal neuration of 

 some Pupipara; frontal lunule and suture almost always distinct; never 

 more than three posterior cells; marginal and submarginal cells never closed; 

 third antennal joint almost always with dorsal arista; bristles of body and 

 legs usually distinct. (Schiz6phor.\.) 3& 



36. Proboscis very rarely elongated; eyes of males usually meeting 37 



Proboscis elongate and slender, often folding; face usually with a groove or 



grooves under the antennae; front broad in both sexes; antennae with terminal 

 style or dorsal arista; no bristles. (Physocephala, Myopa, Zodion, Onco- / 



myia) (PL, 11, fig. 252; PI. 12, fig. 292) CONOPID-S; V 



37. First posterior cell open, no extra vein crossing the anterior crossvein; rather 



small, dull colored species 38 



First posterior cell closed, usually an extra vein between the third and fourth 

 veins; head and usually body without bristles; arista almost always dorsal; 

 usually bright colored flower flies. (Paragus, Syrphus, Eristalis, Helo- 

 philus, Xylota) (PI. 12, figs, 281, 301) SYRPHID^ 



38. Arista terminal; hind tibiae and tarsi dilated, especially in the male; head and 



thorax with bristles. (Platypeza, CaUlmyia) (PI. 12, fig. 285) (CLY- 



THIID/E) PLATYPEZID^ ^ 



Arista dorsal; hind legs not dilated; without true bristles. (Pipunculus, 

 Chalarus.) (PI. 12, fig. 289) {DORYLAIDM) PIPUNCULID^ / 



39. Legs not broadly separated; head movably separated from the thorax; adults 



not ectoparasites upon warm-blooded vertebrates; rarely viviparous, in 

 which case the new-bom larvae are young. (EtTMYiiDiE, Muscoidea, 



Myiodaria.) 40' 



Legs attached to the sides of the body; head small and closely united with 

 the thorax, or folding back into a dorsal groove; adult flics of a leathery or 

 horny structure, often wingless, living parasitically upon warm-blooded 

 vertebrates; viviparous, the new-born larvae well developed, ready for 

 pupation. (Pupipara. Nymphipaea, Eproboscidea, Omaloptera) 79 



40. At least the lower calypter large; posthumeral and intraalar bristles usually 



both present; thorax with a complete transverse suture, posterior callosity 



