108 Annals Entomological Society of America [Vol. XII, 



The barbatus Group. 



The members of this group have a broad mesothorax, quite evenly 

 cun^ed, short-haired all over, especially anterior to the transverse 

 suture. Only a few prominent bristles above the attachment of the 

 wings and posteriorly. Scutellum short-haired on the disc, and usually 

 with not more than half a dozen bristles on the margin, although 

 occasional specimens may have one or two more than this niunber, in 

 most cases there are less. Branching of the third vein never anterior 

 to the base of the second posterior cell, occasionally it is opposite the 

 base of this cell, but in nearly all cases it is plainly beyond, making the 

 second submarginal cell short. The posterior branch of the third vein 

 bends forward, and reaches the costa distinctly before the apex of the 

 wing. 



In some species the male has the costa thickened and expanded on 

 the anterior margin, somewhat before the apex, but in other species 

 this is not the case. 



A species which is typical of this group is what in recent 

 years has been called albibarbis, but here it is considered the 

 same as barbatus which is an older name as indicated in the list 

 of species on another page. 



1. Hypopygium small or of normal size, medium sized to small species, usually 



of slender build, male costa not at all or only very slightly expandecl, 

 female with each abdominal segment black, with posterior" gray border 

 of various widths according to species 2 



Hypopygium distinctly enlarged, large to very large species, male costa 

 rather conspicuously thickened and expanded, female abdomen variously 

 marked, but usually the segments are not black with posterior gray 

 borders, although this is the. case in at least two species 5 



Hypopygium distinctly enlarged, costa not at all thickened and expanded, 

 mystax straw yellow in both sexes, bristles of the thorax and scutellum 

 pale, abdomen uniformly yellowish gray poUinose, male with the apical 

 abdominal segments partly or wholly silvery leucocomus Williston 



2. Gray bands of the abdomen regular and wide, approaching the width of the 



black intervals between them, hypopygium red zonatus n. sp. 



Hypopygium black, gray abdominal bands irregular or very narrow 3 



3. Mystax pale, sometimes with a few black bristles on upper margin, 



barbatus Fabr. 

 Mystax largely bla'?k with pale hairs and bristles intermixed 4 



4. Sixth and seventh segments of male abdomen silvery, pale bands of the 



abdomen brownish gray, with front margin more or less irregular. 



cingulatus Bellardi 



Fifth, sixth and seventh segments of male abdomen silvery; pale bands of 



the abdomen silvery, regular and narrow willistoni n. sp. 



5. Male hind tibiae with an abnormal enlargement 6 



Male hind tibiae normal ■ 8 



6. Wings quite distinctly brown sagax Williston 



Wings hyaline 7 



7. Apical third of the male tibia enlarged... tagax Williston 



Apical half or more of male tibia enlarged armatus Hine 



8. Male seventh abdominal segment entirely silvery dorsally; female fifth 



abdominal segment not silvery 9 



Male seventh abdominal segment clear black on the greater part of the 

 dorsum; female fifth abdominal segment broadly silvery on each side, 

 with a black stripe on the middle of the dor.sum 10 



