28 NOETII AMERICAN DTPTEEA. 



which is at or before the tip in Psi/c/toda, and distinctly be- 

 hind it in Pericoma. In their study, one shoukl use prefer- 

 ably a compound microscope, and it may be necessary either 

 to mount a wing, or at least to remove the scales. Attention 

 should be paid to the shape of the antennae and palpi, as well 

 as the genitalia, legs and wings. Psyehoda alternata Say is 

 our most common species, apparently extending over all the 

 United States. 



S. DIXID.E. 



Rather small, slender, nearly bare species. Proboscis some- 

 what projecting; palpi four-jointed ; antennae long, the basal 

 joints thick, those of the flagellum hair-like, and the joints 

 indistinctly distinguishable. Eyes round, dicho])tic ; no ocelli. 

 Thorax strongly convex, without transverse suture; scutellum 

 transverse; metanotum arched. Abdomen long and slender, 

 composed of seven or eight segments, thickened posteriorly in 

 the male, pointed in the female. Legs long and slender ; 

 coxte somewhat elongated ; tibijB without terminal spurs. 

 Wings comparatively large ; auxiliary vein present, termina- 

 ting in the costa before the middle of the wing; the second 

 vein arises from the first near the middle of the wing and 

 appears to be the beginning of the third vein, Avliich continues 

 its direction while the second arches suddenly forward at the 

 anterior cross-vein and is furcate ; fourth vein furcate ; four 

 ])osterior cells present ; the two basal cells very large ; the 

 anterior cross-vein is placed at the beginning of the third 

 vein, where the second vein curves forward. 



The family Dixidie comprises about a score of known s})ecies 

 belonging to the single genus Dixa. It has been jolaced among 

 tlie TipididcB and Culicidge, but seems best isolated into a sep- 

 arate family. The larvit? are aquatic, resembling those of the 

 mosquitoes. The flies are fouml in bushy, moist places about 

 forests, and have been observed by Winnertz dancing in the 

 air in swarms. 



