NORTH AMERICAN DIPTERA. 



84. Cheeks about one-fourth or less of eye-height (97, 98) . 



Plaglprospherysa. 

 Cheeks nearly as broad as eye-height. . . Baumhaueria. 



85. Eyes bare, or with indistinct hairs. . . 86 

 Eyes distinctly hairy. . Cyrtophlceba. 



86. Sides of face without stout macrochaetae. ... 87 

 Sides of face with one or more pairs of macrochaetae. Paraplagia. 



87. Arista thickened almost to its tip; third vein bristly nearly to an- 



terior cross-vein. ...... Metaplagia. 



Arista not thickened to the middle; third vein bristly less than 

 half way to the cross- vein (62). . . Heteropterina. 



88. Sides of face bare on lower half. ..... 89 



Sides of face with hairs. ...... 140 



89. Vibrissae distinctly above oral margin. .... 91 



Vibrissae on a level with oral margin. . . . . .115 



Vibrissae very vestigial. . . 90 



90. Wings nearly wholly brownish black; black species (58, 59). 



Penthosia. 

 Wings brownish anteriorly only. . . . Clinogaster. 



91. Eyes bare. ....... 92 



Eyes hairy. ....... 109 



92. Penultimate joint of arista more than twice as long as broad. 93 

 Penultimate shorter or only slightly longer than broad. . 94 



93. Proboscis beyond basal articulation at most one and two-fifths 



times the height of head (2) Aphria. 



Proboscis beyond basal articulation at least two and one-third 

 times the height of head (114). . . Cheetog-lossa. 



94. Palpi absent or vestigial (54) Ocyptera. 



Palpi present. ....... 95 



95. Proboscis beyond basal articulation at least one and one-third 



times the height of head. (2) Aphria. 



Proboscis beyond basal articiilation at most one and one-fifth times 

 the height of head. ........ 96 



96. Antennae reaching at least the lowest fourth of face. . . 105 

 Antennae not reaching below the lowest third. ... 97 



97. Vibrissae at less than half the length of the second antennal joint 



above the oral margin. ....... 98 



Vibrissae at least the length of the second joint above the oral 

 margin. ......... 99 



98. Lowest frontal bristles not below the base of the second antennal 



joint (72, 75) Pachyophthalmus. 



Lowest frontals below the middle of second antennal joint (6) . 



Atacta. 



99. Lowest frontals below middle of second antennal joint. . 100 

 Lowest frontals not below middle of second joint. . . 103 



100 Ocellar bristles directed forward. ...... 101 



Ocellar bristles wanting. Belvosia. 



