152 KANSAS UNIVERSITY QUARTERLY. 



of the segments, particularly the second, more or less yellow, usually 

 showing this color only along the sides. Venter yellow. Sixth 

 segment and hypopygium wholly yellow. Coxce yellow, the anterior 

 ones, very long, with a thin row of pale hairs in front; the intermed- 

 iate ones brownish at the extreme base; posterior ones with a single 

 dark bristle on the outer side. Legs and feet wholly yellow; the 

 front tibiae slightly longer than their femora, the first two joints of the 

 fore tarsi are elongate and slender, together longer than the tibia; the 

 remaining three joints very short, subequal. Middle and hind legs 

 and feet simple, but exceedingly slender. Wings hyaline with yellow 

 veins, sixth vein almost obsolete. 



Female. Face scarcely wider; antennae a very little shorter; fore 

 feet fully as long as in the male, but the joints successively shorter, 

 as usual. In both sexes the middle metatarsus is longer than the 

 tibia. 



Length, 2.5-2.8 mm. ; of wing, 3 mm. 



Numerous males and females, Brookings, South Dakota. Common 

 in July on the trunks of trees. I collected it on willow, cottonwood, 

 and box elder. A single male from Florida, sent me by C. W. 

 Johnson, does not seem to be specifially distinct. 



Metapelastoneurus. 



New genus. 



Male. Face wide, convex below; antennae short, the third joint 

 rounded, with a dorsal, plumose arista; fourth vein of the wing bent 

 forward near its tip, ending but a little distance behind the third; 

 hypopygium exserted, about as long as the fifth abdominal segment, 

 bent forward under the venter; at its tip prolonged into four fila- 

 ments which reach the posterior coxas. 



The only essential difference between this genus and Pelastoneurus 

 is in the structure of the hypopygium. The basal segment of the 

 organ in a typical Pelastoneurus {vagans^ is long and slender, and 

 the central portion is also somewhat slender. Besides the small 

 hook-like processes at the tip, — the true grasping organs — the 

 hypopygium also bears two narrow fringed lamellre, arising from the 

 tip at the edge which would be called dorsal were the organ extended 

 behind the abdomen. These lamellae are homologous with those 

 which are so conspicuous in the genus Dolichopus. 



In Metapelastoneurus, the hypopygium differs from that just 

 described in being very short and compact in structure. The basal 

 segment is embeded in the abdomen, instead of forming a peduncle. 

 The central portion is thicker and a third shorter than that just 

 described. The lamellre, however, are most modified of all the parts, 



