214 DIPTERA OF NORTH AMERICA. [PART II. 



compared to balticus Meig., alpinus Wahlb. and callostomus 

 Lw. It can easily be distinguished from balticus by the dark 

 knob of the halteres ; from alpinus by the want of a curved thorn 

 at the end of the fore tibiae ; from callostomus by its more con- 

 siderable size and a comparatively narrower face. 



2. H. pirata LOEW. <j? . Olivaceo-seneus, thorace et scutello cupreo- 

 splendentibus, abdomine virescente, femoribus tibiisque viridibus, tarsis 

 nigris, polline faciei opacse ex fusco ochraceo, pleurarum polline albido, 

 venis alarum cinerascentium nigris, longitudinalibus tertia et quarto, 

 apicem versus paulo convergentibus. 



Metallic olive-brown, thorax and sc.utellum with a copper-colored reflex- 

 ion ; abdomen greenish ; femora and tibi?e green ; tarsi black ; the dust 

 upon the opaque face brownish ochre-yellow ; that of the pleurse whitish ; 

 wings gray with black veins, the third and fourth longitudinal veins 

 somewhat converging towards their ends. Long. corp. 0.15. Long. al. 

 0.240.26. 



SYN. Hydrophorus pirata LOEW, Neue Beitr. VIII, 71, 1. 



Face with brownish-yellow dust, entirely opaque. Palpi black 

 and covered with black hairs, on the upper , side with brownish- 

 yellow dust. Antennae entirely black. Front brownish-black, 

 opaque ; when seen in an oblique direction, it seems as if partially 

 covered with brownish-yellow dust. On the occiput the ground- 

 color is green, however almost entirely covered with grayish- 

 yellow dust, or rendered very opaque. The cilia of the upper 

 orbit are, as usual, black, the dense and hair-like cilia of the 

 lateral and inferior orbits however, yellow. The upper side of the 

 thorax is metallic olive-brown with a copper-colored reflection; 

 the scarcely perceptible dust upon it is brownish-yellow. Scutel- 

 lum with four bristles, shining, copper-colored upon the middle, 

 on the margin green. Pleura? and coxae with whitish dust. Ab- 

 domen more green than the thorax and with a coppery tinge, upon, 

 the greater portion of the last segment and upon the posterior 

 margin of the preceding segments usually beautifully green ; its 

 short hair is blackish, only upon the posterior margin of the first 

 and of the last segment it is pale. Fore coxae on their front side 

 with a very short and delicate whitish pubescence, on their ex- 

 terior margin fringed with black, stiff, but not very strong, bris- 

 tles, of which there are also a few on the tip. Femora slender, 

 green, and covered with thin, almost imperceptible, whitish dust ; 



