454 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.43. 



16. Costa to much beyond wing middle, fringe very short, abdomen orange-red, apically 



blackened, legs wholly yellow aurea, p. 467. 



Costa to slightly beyond middle, fringe longer, abdomen yellow, with lateral black 

 spots or bands on segments, tips of hind femora blackened. 



a, halteres yellow, thorax clear yellow scalaris, p. 467. 



b, halteres brown, thorax brownish yellow cordobensis, p. 467. 



17. Mesopleura with one strong backwardly directed bristle, or with numerous small 



bristles 18. 



Mesopleura bare 19. 



18. Mesopleura with numerous small bristles. 



a. Arista thick and short, barely longer than frons sublutea, p. 468. 



b. Arista thin, distinctly pubescent, and at least one-third longer than 



frons carlynensis, p. 468. 



Mesopleura with one strong backwardly directed bristle (see 14). 



19. First division of costa not longer than the second and third together, the fringe 



short 20. 



First division of costa longer than the other two together 21. 



20. Frons gray -brown, lower pair of post-antennal bristles about one-half as long as 



upper pair, second abdominal segment weakly bristled laterally, first costal 



division shorter than second flava, p. 469 



Frons yellow, darker on vertex, lower post-antennal bristles about one-fourth as 

 large as upper, second abdominal segment with several distinct bristles laterally, 

 first costal division as long as second subflava, p. 469. 



21. Center pair of bristles in first row very much lower on frons than outer pair, and 



directly under them near the eye margins, so that it looks as if there were two 

 rows of two bristles each, instead of one row of four on front of frons; post- 

 antennal bristles of equal size atlantica, p. 470. 



Center pair of bristles in first ro¥,»very slightly lower on frons than outer pair, and 

 further from the eye-margins 22. 



22. Costa reaching to middle of wing 23. 



Costa short of the middle of the wing 26. 



23. First costal division very slightly longer than second and third together, the 



fringe of moderate length and widely placed, fourth dorsal abdominal segment 

 of female with a lateral transverse incision, which appears to divide the seg- 

 ment, at slightly beyond basal third incisa, p. 470. 



First costal division distinctly longer than other two together 24. 



24. Frons, antennae, and halteres yellow; costal fringe long, first costal division more 



than twice as long as second lutea, p. 471. 



Frons and antennae brown or black 25. 



25. Small species, about 1 mm. in length, first costal division about one and one-half 



times the length of second; frons, antennae, and halteres brown; fringe of 



moderate length but sparse and delicate; halteres brown obscura, p. 471. 



Larger species, about IJ to 2 mm. in length, first costal division about twice as 

 long as second, fringe extremely long and strong, halteres yellow. 



evarthse, p. 472. 



26. Frons black or brown 27. 



Frons and antennae yellow, sometimes infuscated above on frons, and at tip of 



antennae straminipes, p. 474. 



27. Antennae yellow; hind tibiae without distinct setulae straminea, p. 472. 



Antennae black or brown 28. 



28. Lower post-antennal bristles but slightly smaller than the upper, thorax reddish 



yellow, fifth segment of abdomen in female about one-third as long as fourth, 



seventh segment pale whitish yellow fungorum, p. 473. 



Lower post-antennal bristles about half as large as upper, generally less; fifth 

 segment in female not shortened 29. 



