221 



tarsi, or a female that does not have these bristles. It is prob- 

 able that this character may be sexual in other species besides 

 this one. In this revision I have placed the female in the sec- 

 tion with the tarsal spines present. 



Pupa. — Length : male, 5.5 mm. ; female, 6-7 mm. Yellowish 

 brown, slightly shining. Thoracic respiratory organ simple, 

 rounded at base, becoming very slightly broader and dis- 

 tinctly flattened as it nears the apex ; viewed from the ventral 

 side the thickened part of the pupa, to the apex of the wing 

 cases, is as long as the next four segments together; there 

 are seven segments beyond the thickened part on the ventral 

 side, the last segment ending in two sharp points. For 

 details of pupa see Plate XIII, Figures 1, 2, 3, and 4. The 

 two small sub-basal i)rojections on the dorsal surface of the 

 abdominal segments are represented on the ventral surface 

 by a slight transverse raised ridge longipenriis Loew. 



Originally described from Pennsylvania. 



The pupa of this species were found by C. A. Hart floating 

 at the surface of the water in the Illinois River at Havana. 

 They are capable of slight movement in the water by means 

 of the abdomen. 

 9. Only one spine on the fore femur, the other femora bare. 



Female. — Black, the head reddish brown, first joint of antennse 

 and bases of the next nine, stems of the halteres, and the legs 

 yellow ; coxae, bases of mid and hind femora, and of their 

 tibiae, also the last two tarsal joints, black. Mesonotum 

 scabrous, pleurae and abdomen polished. Fore femur with 

 one spine on the middle of the under side ; the hind femora 

 considerably thicker than the others. Tarsal claAvs large, 

 subequal. Vein 4 forked slightly before the cross vein. 

 Length, 3 mm. (Mexico) scahra Coquillett. 



I have not seen this species. It should be very readily distin- 

 guished from any other described form in this genus by the 

 single bristle on the femora. 



— At least the hind or mid femora with spines 10 



10. Mesonotum without distinct pollinosity 11 



— Mesonotum with dense pollinosity 12 



11. Mesonotum glossy black; hind tibia entirely black; third vein from 



the cross vein (Ro) to its apex distinctly shorter than the section 

 of the media bordering the posterior side of the closed cell at 

 wing-middle, the third vein reaching about five sixths of the 

 distance to the wing-tip. 



Female. — Glossy black. Antennge yellowish, darker at apex; 

 face brown; pleuraj brown-black, becoming yellowish below 

 wing base. Legs yellow ; fore coxro brown, mid and hind 

 pairs black; apical half of the hind femur, the whole of hind 

 tibia, and the apices of the last two tarsal joints black. 



