224 ERNEST A. BACK. 



yellow. Front a little polished in the middle, thinly grayish-brown 

 pruinose. Face rather gray pruinose, somewhat polished in the mid- 

 dle; pile and mystax white. Dorsum of the thorax polished, but 

 mostly concealed beneath golden pubescence. Pleurae densely white 

 pruinose, with two polished spots, the one on the mesopleurae, the 

 other in front of the halteres. First five segments of the abdomen 

 with a small silvery spot on the hind angles; elsewhere polished; 

 sixth segment a little longer than the fifth, gradually tapering." 



Type. — University of Kansas. One male specimen. 

 Habitat. — Western South Dakota (type). 

 I have not seen this species. 



Psilocjiriis midiusculus (PI. IV, fig. 11; PI. IX, fig. 4). 



Psilocurus niidinsculus Loew, Berl. Ent. Zeit., XVIII, 370, 

 1874. 



(^ 9- — Length 8-10 mm. — Ground color of head and thorax black, 

 but everywhere densely clothed with a grayish or brassy pubescence; 

 the abdomen black above, merging into a brownish or reddish color 

 on the anterior, posterior and lateral margins; sometimes almost 

 wholly reddish-brown; the lateral margins covered with a white 

 bloom which on the posterior margin of each segment, except the 

 first, extends in a narrowing line up onto the tergum. Legs more or 

 less reddish-yellow; all the femora above with a black fascia. 



Face and front grayish-yellow pruinose; the occiput brownish, 

 grayish along the orbits, above with a row of bristles, which imme- 

 diately behind the vertex are black, but smaller and paler on the 

 outer orbits. Mystax and the long bristle of the first antennal segment 

 sordid yellow; the beard scant, white. Antennse short, the first seg- 

 ment reddish, the others black; the third hardly as long as the first 

 two taken together, roundish oval, and bearing on the upper distal 

 portion a very small spine; the style rudimentary. Dorsum of thorax, 

 scutellum and upper portion of pleurae concealed beneath a dense 

 clothing of fine appressed brassy-yellow pubescence; the rest of the 

 pleurae except a polished stripe, coxae and the metanotum, grayish-white 

 white, in certain lights silvery white, pruinose. The three bristles on 

 either side of the dorsum and the (usually) four bristles of the scutellum, 

 black. Halteres yellow; the trichostical hair pale. Abdomen as 

 described above in synopsis, but subject to considerable individual 

 variation, being sometimes nearly black, again more reddish, but 

 always with the broad posterior lateral margins of the segments and 

 the narrow line on the posterior margins, whitish pruinose. Abdomen 

 apparently bare, but in truth clothed with very fine pubescence, black 

 upon the dark areas, white upon the white pruinose areas; the char- 

 acteristic bristles pale, three arranged in a transverse line on the first 

 segment, two on the following two segments and one on the remaining 



