912 CHARLES PauL ALEXANDER 
11. Second anal vein arcuated, before its tip bent strongly toward the first. [Erioptera 
holotricha O. S. Proc. Acad. Nat. Sci. Phila., p. 226. 1859.]....O. holotricha (O. 8.) 
Anal veins divergent. [Trans. Amer. Ent. Soc., vol. 42, p. 140, pl. 10, fig. 6. 1916.] 
O. palpalis Dietz 
13 
CULO: nee ge Se hate Peg veh ad Conlones Uo Oe ee be hl eee 19 
13. Second anal vein arcuated, before its tip bent strongly toward the first.............. 14 
Anal: veins divergent, (2). 22. ehc. 8k bs ble Sa bhis Roce oe ee eee 18 
14.°"Thorax reddish. 22. .c. ca bebe ce oe oe be sie eens De bt 15 
Thorax not reddish. A050's5 206 so.) ee Doig be oe oe 16 
15. Mesonotum with a dark median line; male hypopygium with two pleural appendages | 
which are almost straight; gonapophyses elongate, black, profoundly bifid; penis 
guard not trifid. [Rhypholophus rubellus O.S. Mon. Dipt. N. Amer., part 4, p. 144, 
Dlaletfies 15592 18695] r (Plate XexexaliVe G05) eee O. rubella (O. 8.) 
Mesonotum without a dark median line; male hypopygium with the pleural appendage 
a single curved hook; gonapophyses strongly curved, entire hooks; penis guard trifid 
at apex. [Can. Ent., vol. 49, p. 24-25. 1917.] (Plate XXXIV, 59.) 
O. nimbipennis Alex. 
16. Stigma distinct, dark brown, the marking continued down onto the cord. [Erioptera 
meigentt O.S. Proc. Acad. Nat. Sci. Phila., p. 226. 1859.] (Plate XXXIV, 61.) 
O. meigenii (O. 8.) 
Stigmaindistinctsor lackingss 050 22,4263. .c tee on ee eee 17 
17. Thorax and antennae light yellow.. [Rhypnolophus parallelus Doane. Ent. News, 
Vols 9! 2202: el 9088 erie eee pe a gee O. parallela (Doane) 
Thorax brown, with a grayish pruinosity and a rather broad darker stripe; antennae 
brown. [Trans. Amer. Ent. Soc., vol. 42, p. 141. 1916.].......... O. perplexa Dietz 
18. Mesonotum with a darker line on either side; ninth sternite produced into a median 
spatulate lobe. [Trans. Amer. Ent. Soc., vol. 42, p. 142-148, pl. 10, fig. 8. 1916.] 
O. bilineata Dietz 
Mesonotum reddish brown with a median brown stripe; ninth sternite produced into 
two flattened lobes that project far caudad. [Trans. Amer. Ent. Soc., vol. 42, p. 143- 
1442 pl: LO} fig Or AGI Eee ales oe ne eee O. deviata Dietz 
19. Anal veins convergent: ssi: s6 session onde sas bedasekhs San GG eRe eee eeeee 20 
Anal veins: divergent... s\.) e065 ce Sache nb Belg eside ck oo ose ee inode Dil 
20. Segments of flagellum shorter, without pale apices. [Can. Ent., vol. 49, p. 25. 1917.] 
(Plate XeX XeW31633) meus tee hee noon ee ee aero eee O. mesocera Alex. 
Antennal segments elongated, the segments attenuated and the apices pale. 
[Rhypholophus monticola O. S. Mon. Dipt. N. Amer., part 4, p. 145. 1869.] 
(Plate XOXO VS 1628) aes ed ey ately Gear be Soi oer rr O. monticola (O. 8.) 
21. Reddish brown; mesonotum with an indistinct brown median stripe. [Trans. Amer. 
Ent. Soc., vol. 42, p. 144-145, pl. 10, fig. 10. -1916.].............. O. divergens Dietz 
Dark brown; mesonotum with three darker brown stripes. [Can. Ent., vol. 49, p. 26. 
L9N7 A) (Plate SXeXexiVE (642) Sea ee a eee es Say ee O. megacera Alex. 
(O. megacera is probably the same as O. divergens, the latter name preoccupied 
by O. divergens Coq. [1905].) 
The small flies that make up this characteristic genus are very com- 
mon, appearing in small swarms under overhanging ledges, along the 
lower face of an inclined tree, or in similar situations. The early spring 
species are Ormosia innocens, O. nubila, O. meigeniz, O. holotricha, and 
others; O. apicalis, O. megacera, and O. mesocera occur in early summer; 
O. nigripila, O. nimbipennis, O. monticola, and O. abnormis are late 
