12 PROCEEDINGS OF THE NATIONAL MUSEUM vol.76 



down from the eye, behind this the ground color is whitish and the 

 hairs are conspicuous and white. Dorsum of thorax shining black 

 with a large polished, bare space encircled by yellowish hairs in front 

 of the suture on each side, another directly behind the suture which 

 is divided by a fine line of yellow hairs; the middle of the thorax in 

 front is also bare and polished ; the central part of the thorax is rather 

 densely covered with yellowish hairs and also pollinose in ground 

 color; these hairs extend on the scutellum close to the side, leaving 

 the large, globose, polished, central portion bare except for two pairs 

 of black bristles and a very few yellow hairs which are perhaps absent 

 in some specimens. All the yellow hairs of the dorsum are quite 

 stout ; the dorsocentral bristles are quite black and somewhat irregular 

 in number, but there is always at least one before the suture ; in most 

 of the Sioux City specimens some of the hairs in the middle region 

 before the suture are distinctly black. Pleurae yellowish brown in 

 ground color, covered with pale pollen and with longer whitish hairs, 

 some of which are on the pteropleura and upper edge of sternopleura; 

 the lower and hind portion of the sternopleura is bare and shining. 

 Halteres yellow; calypters whitish; postscutellum with an opaque 

 blackish ridge above, immediately under the scutellum, below this 

 covered with pale pollen except close to the junction of the abdomen. 



Abdomen black in ground color, the hairs entirely white except a 

 few at the hind edge, the second to fourth tergites are short, not 

 reaching the sides of the abdomen which are covered with a swollen 

 expansion of the soft membrane usually connecting the tergites and 

 sternites. This membrane is remarkably enlarged, occupying the 

 entire lateral portions of the abdomen and apparently replacing most 

 of the area of the sternites below as well as invading the dorsal side 

 of the abdomen to a considerable extent. It has several deep longi- 

 tudinal grooves visible from the side, giving much the appearance of 

 the abdomen of a female distended with eggs. 



Legs dark yellow, the front femora with conspicuous pale hairs on 

 the basal three-fifths, the apical remaining part with black hairs. 



Wing with diagonal apical mark not quite filling the space to the 

 costa in front of the tips of the second and third veins and entirely 

 separated from the large oblique band on the middle of the wing which 

 is broadly joined toward the costa with the subbasal band as usual. 

 Base of the wing quite blackish a little farther than the humeral 

 crossvein; the apical and subapical dark bands have a decided yel- 

 lowish tinge between the second and fourth veins. 



Female. — Abdomen entirely normal without any trace of the soft 

 lateral membranes, the sternites and tergites occupying the usual 

 position. Ovipositor large, its main segment almost as long as the 

 remaining part of the abdomen, shining brown to black in color. 

 The palpi and third antennal joint are dark brown in one specimen. 



