54 NORTH AMERICAN DIFPERA. 



food is wholly consumed. Frequently the larvae are found 

 free in the earth, however, where their transformation takes 

 place. The eggs are laid about grass stems, or in the crevices 

 of decaying trees infested by larvae of other insects. 



TABLE OF GENERA. 



1. Marginal cell of wings open. . 2 



Marginal cell closed 3 



2. Third joint of antennae with an arista or aristiform style ; abdomen 



slender; pulvilli wanting. . . . LEPTOGASTER Meigen. 

 Antennae not with an arista ; usually with a thickened style. 



DASYPOGONIN^E. 



3. Antennae with a terminal bristle. . . . . . ASILIN^E. 



Antennae not with a terminal bristle. .... LAPHRIN.*:. 



DASYPOGONIN^E. 



1. Front tibiae with a terminal, claw-like spur. . . .28 

 Front tibiae not with a terminal, claw-like spur 2 



2. Pulvilli rudimentary or wanting. . . . ABLAUTUS Loew. 

 Pulvilli normal 3 



3. Head narrow, about as high as broad ; face narrow above, broader and 



swollen below, in large part covered with hair; large, elongate 



species . ' . . 4 



Head very obviously broader than high 6 



4. Antennae with a terminal style 5 



Third joint of antennae long, without style; fourth posterior cell closed 



before the border of the wing; black species, with or without red on 

 the abdomen. OSPKIOCEKUS Loew. 



5. Style about half the length of the third antennal joint. 



SCLEROPOGON Loew 



Style about a sixth or an eighth of the length of the elongated third 

 joint STENOPOGON Loew. 



6. Fourth posterior cell closed before the border of the wing. . 7 

 Fourth posterior cell wide open, rarely nearly closed. ... 13 



7. Antennae much elongate, apparently composed of five joints. . 14 

 Antennae not elongate, composed of three joints, without terminal 



style. 8 



8. Face bare, except on oral margin. . t \ . . . 9 

 Face pilose or hairy, more convex. . . . . . . 10 



