36 NORTH AMERICAN DIPTERA. 



2. Three posterior cells ..... BITTACOMORPHA Westwood. 

 Four posterior cells. ..... PTYCHOPTERA Meigen. 



1. Legs long and slender, especially the tarsi ; anterior branch of the 



second vein absent, obsolete or perpendicular, the rhomboid cell 

 more or less square. . . : " . . . . . . 2 



Legs not unusually slender, anterior branch of second vein present and 

 oblique. .--'.-_ ........ 5 



2. Antennae thirteen-jointed ; male forceps complex. 



DOLICHOPEZA Curtis. 

 Antenna? with less than thirteen joints; male forceps small, simple. 3 



3. Fifth posterior cell not in contact with discal cell. 



MEGISTOCERA Wedemann. 

 Fifth posterior cell in contact with discal cell ..... 4 



4. Head on a neck-like prolongation of the thorax; seventh vein short 



running into the anal angle. . BRACHYPREMNA Osten Sacken. 

 Head more closely applied to the thorax ; seventh vein terminates in the 

 margin at some distance from the anal angle. 



TANYPREMNA Osten Sacken. 



5. Antennae of $ pectinate or sub-pectinate. . ... . 6 



Antennae not pectinate. . . . ..... 7 



6. Ovipositor of 9 long, sword-like. . . . XIPHURA Brulle. 

 Ovipositor of $? l n e but not sword-like. . CTENOPHORA Meigen. 



7. Three posterior veins arising from the discal cell, the two anterior 



sometimes arising together but the petiole always short. 



PACHYRRHINA Macquart. 



Two posterior veins arise from the discal cell the anterior one furcate, 

 petiole always of considerable length. . . . . . 8 



8. Antennae serrate; northern species. . .. STYGEROPIS Loew. 

 Antennae not serrate below. ........ 9 



9. Marginal vein wanting, but one marginal cell, antennal joints short with 



minute bristles. . . . . . . HOLORUSIA Loew. 



Two marginal cells. ......... 10 



10. Abdomen slender, very long; antenna? composed of twelve joints. 



LONGURIA Loew. 

 Abdomen less elongate; antennae with thirteen joints. TIPULA Linne. 



