442 



14, Plate XXX ; that the ventral blood-gills are absent; and that there 

 are six sensory hairs in each of the dorsal tufts. 



Pupa. — Length, 6 mm. Yellowish brown. Frontal tubercles very 

 small. Thoracic respiratory organs ending in numerous white hairlike 

 filaments. Second abdominal segment with a series of about six 

 transverse rows of short setulae forming a band near the base on the 

 dorsal surface, and the usual apical band of stronger black setulae ; 

 segments 3-7 w^ith the band near base, that on 7 being rather indistinct, 

 segments 4-6 with short setulae on dorsal surfaces which become more 

 numerous near apices of segments, forming a slight band; lateral 

 apical process of eighth segment ending in a sharp thorn, its sides with 

 several shorter thorns (PI. XXXI, Fig. 16) ; apical abdominal appen- 

 dages more than three times as long as broad, densely fringed. 



Imago; Male. — Black, opaque. Head fuscous, face and antennal 

 flagellum yellowish; plumes of antennae fuscous. Thorax black, an- 

 terior lateral angles and lateral vittae deep brown, the median vitta and 

 sometimes the median portion of mesonotum behind it as w-ell as the 

 inner portion of lateral vittae pale reddish brown ; lateral vittae with 

 dense whitish pruinescence ; scutellum pale brown; postnotum black. 

 Abdomen velvety black, the anterior lateral angles of the segments of 

 the basal half sometimes brownish; hypopygium yellow'ish. Legs pale 

 yellow ; coxae and generally also the greater part of fore and mid 

 femora blackened. Wings clear, veins yellow, cross vein unclouded. 

 Halteres yellow, sometimes slightly darkened apically. Hairs on body 

 and legs pale yellow. 



Frontal tubercles indistinguishable. Pronotum linear on upper 

 half, not extending to upper margin of mesonotum. Hypopygium as 

 in Figure 16, Plate XXXHL Legs slender; fore tarsi without long 

 hairs, basal joint nearly one half longer than fore tibiae (53 : 37) ; mid 

 and hind legs long-haired. Third vein ending nearly at wing-tip; 

 cubitus forking very slightly beyond cross vein. 



Female. — Similar in coloration to the male except that the mid 

 tibiae and apices of tarsi are usually distinctly browned. 



Hairs of antennae comparatively long, greatly exceeding the length 

 of the apical joint. In other respects similar to the male. 



Length, 3-4.25. mm. 



Illinois locality, Thompson's Lake, near Havana, reared from 

 larvae dredged from a depth of eight and a half feet April 28 and May 

 I, 1914 (C. A. Hart and J. R. Malloch). The adults emerged May 12 

 and 14 respectively. 



One reared specimen is a hermaphrodite, the bisexual characters 

 lying in the antennae, the basal third of the flagellum of both consisting 



