30 BULLETIN 116, UNITED STATES NATIONAL MUSEUM. 



47. Middle and hind femora each with three preapical bristles; middle tibiae with 



one bristle below, which is unusually long. .No. 47, partitus Melander & Brues. 

 Middle and hind femora each with one preapical bristle 48. 



48. Hind tibiae wholly black, the extreme base may be yellow 49. 



All tibiae yellow, at least at base on upper edge for a considerable distance; pos- 

 terior pair black at tip 50. 



49. Middle tibiae yellow; front covered with white pollen, which almost conceals the 



ground color No. 28, agronomus Melander and Brues. 



^Middle tibiae black with more or less yellow on upper edge, sometimes yellowish 

 brown; front shining, metallic No. 24, acuminatus Loew. 



50. Third antennal joint large for a female, somewhat triangular, pointed, the arista 



inserted close to its tip No. 40, angusticonds, new species. 



Third antennal joint of normal size, if large the arista distinctly dorsal 51. 



51. First antennal joint yellow below No. 27, conspectus, new species. 



Antennae Avholly black, or very nearly so 52. 



52. Middle tarsi wholly black (Alaska), No. 219, new species. 



Middle basitarsi largely yellow 53. 



53. Middle tarsi yellow with the tips of the joints broadly black, their anterior surface 



with silvery pollen No. 50, remipes Wahl. 



Middle tarsi black from the tip of the first joint 54. 



54. Wings with the third and fourth veins convergent toward their tips, where they 



are scarcely more than half as far apart as at the bend in fourth vein. 



No. 35, convergcns Aldrich . 



Thii-d and fourth veins but little convergent beyond the bend in last section of 



fourth vein 55. 



55. Black at tip of posterior tibiae extending along the inner sui'face nearly or quite 



to their base 56. 



Black at tip of posterior tibiae not extending up the inner surface to any great 

 extent, usually not at all 58. 



56. Small hairs on anterior surface of fore coxae wholly black or very nearly so. 



No. 45, albiciUctus Loew. 



Small hairs on fore coxae partly white, these white hairs conspicuous on outer 



half of the anterior surface 57. 



57. Fore tarsi scarcely as long as their tibiae, fifth joint as long as third; orbital cilia 



silvery white No. 48, setifer Loew. 



Fore tarsi as long as their tibiae, third joint as long as fourth and fifth taken to- 

 gether; orbital cilia white but tinged with yellow. .No. 26^, burnsii, new species. 



58. Orbital cilia wholly black, except one or two near the proboscis 61. 



Many of the lower orbital cilia pale 59. 



59. Hind femora with short but distinct black cilia on lower inner edge. 



No. 45, albidhatus Aldrich. 

 Hind femora without cilia on lower inner edge 60. 



60. Small species with the bend in last section of fourth vein distinctly before its 



middle No. 44, xanthocnemus Loew. 



Moderately large species, with the bend in last section of fourth vein just before 

 its middle No. 37, harbicauda, new species. 



61. Last section of fourth vein only a little bent No. 41, oequalis, new species. 



Last section of fourth vein with a small but rather sharp bend. 



No. 46, alacer, new species. 



62. Middle femora largely or wholly yellow, anterior and posterior ones black on 



basal half or more 63. 



Anterior and middle femora yellow, posterior pair black 67. 



Middle and posterior femora largely yellow, anterior ones black on basal half 



or more 68. 



