440 NEW YORK STATE MUSEUM 



longer than all the rest taken together. The palpi are some- 

 what shorter than the antennae, four jointed (besides a small 

 basal piece), the first joint shorter, the fourth longer than the 

 other two. Dorsum of the thorax black, subshining, with a 

 faint cinereous bloom, covering the surface excepting the three 

 slightly raised longitudinal stripes, which are deep black, and 

 on which are arranged some scattered black setae; scutellum 

 dark brown, with black setae; metanotum and pleura black, 

 the latter with a gray bloom; abdomen black, longer than the 

 wings in fresh specimens, covered with fine brown or black 

 hairs, posterior margins of the segments narrowly cinereous. 



Genitalia conspicuous and rather complex [pl.47, fig.8 dor- 

 sal, fig.lO ventral, view]. The apical joint of the appendages, 

 triangular in outline with a sharp point; the basal joint with 

 a pointed process attached near its base on the inner side, 

 mesad of which are two smaller pointed projections. The dor- 

 sal spur is nearly straight and spikelike. Legs uniformly 

 fuscous, all the fourth tarsal joints shorter than the fifth, 

 tarsal claws simple. Wings broad, and nearly as long as the 

 abdomen in fresh specimens; usually longer than abdomen in 

 dried specimens; cinereous in color, the anterior veins conspic- 

 uous, brownish or black; media and cubitus pale, posterior mar- 

 gin very delicately ciliate. Halteres usually pale, in some spec- 

 imens pale brownish, the knob triangular in outline. Length 

 8.5 to 5mm. 



Female. Cinereous black, front and epistome cinereous, eyes 

 but slightly excavated at base of antennae; palpi and antennae 

 fuscous, the latter with eight joints counting the disklike basal 

 joint, short haired [fig.7] ; scutellum hemispherical, dark brown, 

 with black setae; abdomen fuscous with short brown hairs, 

 posterior margin of the segments darker except on the extreme 

 edge, which is pale yellow; genitalia small, brown and leaf like; 

 legs fuscous; claws simple; wings broad, and longer than the 

 abdomen; anterior veins black; media and cubitus pale; vena- 

 tion ae in the figure. Length 3.5 to 5 mm. All else as with 

 the male. Described from bred and captured specimens. 



Larva .[pl.48, fig.9-L3]. The larvae were taken in company 

 with the larvae of T h a 1 a s s o m y i a f u s c a among the 

 algae on the surface of rocks over which the water flows rap- 

 idly. In its pale green color, its general appearance, and even 

 in many details it greatly resembles T h a 1 a s s o m y i a 

 f u s c a . The dorsal sclerite of the head is shaped like that 

 of the last mentioned species shown on plate 50, figiire 4; 

 with two pair of marginal setae, but the hindmost pair are 

 situated farther back than in T h a 1 a s s o m y i a f u s c a . 

 On the lateral sclerite there is one seta near the base of the 



