OF PHILADELPHIA. 65 



Antennae black, first joint "of the style longer than the second ; 

 wings dusky, hyaline, nervures as in Meigen's fig. 10, pi. 20, ex- 

 cepting that the central cellule is rather more elongated ; tergum 

 velvet-black, a cinereous band at base, a linear one near the mid- 

 dle, and a dilated silvery one on the middle, tip ©f the tergum 

 cinereous ; venter somewhat livid, immaculate. 



Length % two-fifths of an inchj ? half an inch. 



Found sometimes in sandy districts. The ground-color of the 

 body is black, but this color is concealed by a pruinose covering. 



[This and the next species belong to Stichopogon Loew. — 

 Sacken.] 



4. D. ARGENTEUS. — Cinereous, immaculate ; poisers paler yel- 

 lowish. 



Inhabits Pennsylvania and Maryland. 



Antennfe black, second joint as long, or slightly longer than the 

 first ; first joint of the style longer than the second, which is aci- 

 cular and minute; mystax and hair of the genae, pure white; 

 vibrissas [52] none; wings hyaline, nervures light brown, ar- 

 ranged as in Meigen's fig. 11, pi. 20. 



Length from three-tenths to seven twentieths of an inch. 



Like the preceding insect, the ground color is black, but this 

 color is concealed by a universal pruinose covering, which has 

 almost a silvery brightness when the animal is living and under 

 the influence of the sun's rays. 



5. D. POLiTUS. — Tergum blackish-blue ; posterior half of the 

 wings fuscous. 



Inhabits Pennsylvania and Maryland. 



Hypostoma and front golden-brown, mystax and vibrissae yel- 

 lowish-brown ; vertex brown; genaj pure white; antennce black, 

 first joint of the style longer than the second, which is acicular and 

 minute ; thorax golden-brown, a double black line abbreviated be- 

 hind, and a lateral broad dusky line approaching behind near to 

 the scutel ; feet rufous, thighs black ; wings, basal half hyaline, a 

 hyaline spot on the carpus, and a smaller obsolete one near the 

 apex; nervures arranged nearly as in Meigen's fig. 11, pi. 20; 

 tergum fine blackish-blue, the segments with lateral marginal cine- 

 reous triangles. 



Length nine-twentieths of an iTich. 

 1S2.3.] 5 



