21G ERNEST A. BACK. 



among these five " pollens" specimens we find that the color 

 of the antennae, legs and abdomen is not constant, and the 

 yellowish color of the bloom is only such as we might expect, 

 and often find, in the female of a dark male. The fact that 

 these specimens and the specimens of morosum came from 

 Dallas and that Loew made his description of morosum from 

 a single male and female, has its weight in considering a 

 species subject to variation. 



These "pollens" specimens are of the same size as morosum 

 with similar, though less intensely black, wings, and the an- 

 tenna? and legs are reddish-brown. In one specimen the third 

 antennal segment is black. The bloom follows the same pat- 

 tern as in the typical morosum, but is yellowish, not white. 

 In morosum the bristles of the palpi, antennae, front, occiput, 

 legs and many on the thorax are black; in "pollens" the 

 bristles are everywhere pale yellow or sordid white except on 

 the legs, where they are of the same reddish color. The 

 abdomen is reddish -brown ; in several specimens more reddish 

 than in others, but in no case is the red color so sharply 

 marked and defined as in the female type of morosum. One 

 specimen has the tergum of the abdomen throughout yellow- 

 ish-red. 



ARCHILESTRIS. 



Archilestes Schiner, Verh. Zool.-Bot. Ges., XVI, 672, 1866. 

 Archilestris Loew, Berl. Ent. Zeit., 1874, 377; change of name. 

 Archilestris Osten Sacken, Biologia, Dipt., I, 169, 1887; note. 

 Archilestris Williston, Psyche, V, 259, 1889. 



Face broad, little swollen on oral margin and thence grad- 

 ually receding to antennae; bare, except a single row of bristles 

 on oral margin; facial orbits parallel, front not widened above, 

 but frontal orbits slightly emarginate, but not as much so as 

 in Microstylum nor with as many short bristles. Segments 

 1 and 2 of the antennae subequal, cylindrical, with short 

 bristles above and below; segment 3 longer than segments 1 

 and 2 taken together, broad at base, gradually tapering to 

 tip, style barely perceptible. The third segment on its upper 

 side toward the tip bears a few short bristles. Proboscis as 

 long as the height of the head. Thorax normal. Abdomen 



