NORTH AMERICAN DIPTERA. 151 



]:.'. — Three veins proceeding from discal cell in front, the upper two sometimes 

 approximated at base, or actually united and petiolate, but the i)etiole 

 for pra^furca) so short that it never reaches the fifth part of the fork in 



length Pachyrrliiua. 



Only two veins proceeding from the discal cell in front, the upper one always 



forked, but the prsefurca always longer than fifth part of fork 13. 



13. — Only one marginal cell, the marginal cross-vein absent; last section of sec- 

 ond vein strongly arcuated towards third vein ; antennal joints minutely 



bristly HoIoruMia. 



Two marginal cells 14. 



14. — Abdomen very long and slender ; antennae 12-jointed LiOngiirio. 



Abdomen not so elongate; anteuuse 13-jointed 15. 



15. — Antennae serrate beueath, rather thickened ; boreal species.. Stygeropis, 



Antennae not serrate Tipiila. 



16. — Second vein furcate, therefore two submarginal cells present* 33. 



Second vein simple, never furcate, therefore never more than one submar- 

 ginal cell present 17. 



17. — Antennae 14-jointed ; if .sometimes apparently IS-jointed, then the proboscis 



never longer than head (subfam. Limnobina) 30. 



Antennae 16-jointed ; or if only 12- or 15-jointed, then the proboscis nearly 



as long as body, or an extra marginal cross-vein in wing 18. 



18. — Tibije with spurs at tip; first usually ending in second (subfam. Cylindro 



tomina) 19. 



Tibi* without spurs at tip; first vein ending in costa (subfam. Limnobina 



anomala) 22. 



19. — Antennal joints almost cylindrical, those of flagellum longer than wide: 



head smooth 20. 



Antennal joints rounded, those of flagellum not longer than wide; head 



and thorax punctured Triogiiia. 



20. — Yellow, black -striped and spotted species 21. 



Species with brownish body and grayish head and thorax.. I'lialacrocera. 



21. — Five posterior cells; small cross-vein present <'yliii<lroloiiia. 



Only four posterior cells; submarginal cell in close contact at base with 



di.scal cell, the small cross-vein therefore wanting Liiogina. 



22. — No submarginal cell ; rostrum longer than head and thorax together, an- 

 tennae 12-jointed Toxorrliiiia. 



Submarginal cell present 23. 



23. — Rostrum of % quite as long as body, somewhat shorter in 9 ; antennae. 15- 

 jointed ft^Iepliaiitoinyiai. 



Rostrum never so long as head and thorax together 21. 



24. — Discal cell present 25. 



Discal cell absent Elliptera. 



25. — No marginal cross-vein 26. 



Marginal cross-vein present (faint in Antocha) 27. 



26. — Rostrum slightly longer than head Khaiiipliiilia. 



Rostrum shorter than head .\tarba. 



* Do not mistake a second (outer) marginal cross-vein in Paratropesa for a 

 branch of second vein; this genus is included in next division with second 

 vein simple and only one submarginal cell. 



TRANS. AM. ENT. SOC. XIX. JUNE, 1892. 



