5G BULLETIN 31, UNITED STATES NATIONAL MUSEUM. 



bluish black, in the female more metallic blue, with thiu, whitish dust^ 

 nearly perpendicular in protile with a prominent, well-defined tubercle, 

 and a smaller one below it. Frontal and vertical triangles with black 

 pile ', front in the female with black pile, except at the vertex. Dorsum 

 of thorax with three opaque stripes in the male, wholly bright shining 

 metallic green in the female. Scutellum shining bluish metallic green. 

 First segment of the abdomen shining black ; second segment with an 

 anterior black cross-band, convex or dilated in the middle behind; in 

 the male the remainder of the second segment, the third, and the an- 

 terior part of the fourth, are orange yellow; in the female on the poste- 

 rior angles of the second with smaller, of the third with larger, black 

 spots, the fourth and fifth segments with an interrupted, anterior, not 

 broad, cross-band. Legs in the male black, with the base of all the 

 tibiae yellow ; the front metatarsi extraordinarily dilated, and with a 

 process directed inward, the remaining joints as usual; the middle 

 metatarsi also considerably dilated, the remaining joints successively 

 less so ; i)osterior metatarsi a little thickened, somewhat elongate. In 

 the female the legs are reddish yellow, the front tarsi, the last four 

 joints of the middle tarsi, a ring on the hind tibiae, and the hind tarsi, 

 black, sometimes also a less distinct ring on the hin<l femora; in struct- 

 ure the legs show no peculiarities. Wings tinged with reddish brown, 

 darker in the middle. 



Two specimens firom Holland (v. d. Wulp), a single female specimen 

 from Washington Territory (Morrison), and a female from Labrador 

 (Henshaw). 



PLATYCHIRUS. 



Platycheirus St. Fargeau and Serville, Eucycl. Meth.. x, 513, 1825. 



Medium sized to rather small species, elongate, nearly bare, black or 

 metallic green, with yellow, reddish, or whitish yellow spots on the 

 abdomen. Wholly like Melano.stoma, except in the structure of the 

 legs. In the male the tibi;« are more or less dilated in the front pair, 

 the front metatarsi always, and the remaining joints more or less, so; 

 in the female the front tibiae and metatarsi, though not dilated as in 

 the male, are comparatively broader than those in Melanostoma. 



TABLE OF SPECIES. 



1. — Front tibia; in the male gradually dilated from the base, the tarsi gradually de- 

 creasing in width from the base to the tip ; profile of the face only gently 

 concave above the tubercle, the latter small ; cheeks convex below . . 2 

 Front tibia? of the male slender, suddenly dilated at the tip, metatarsi much 

 dilated, the remaining joints but slightly so ; the front femora in the male 

 with a thick row of hairy pile on the posterior side ; face in both sexes 

 with a conspicuous tubercle ; cheeks concave below .... peltatus 



