284 DIPTERA OF NORTH AMERICA. [PART IV. 



allied to Bhaphidolabis, but the body is less slender, the male 

 genitals not club-shaped and of a different structure ; the feet 

 comparatively much shorter. The venation is pretty much the 

 same in both genera, as the comparison of the descriptions will 

 show, except that Plectromyia has only four posterior cells, and 

 that the subcostal cross-vein is less near the root of the wing. 

 The discal cell is absent in all my specimens. 



The name of the genus is derived from Ttirjxtpov, spur, and pvia, 

 fly, in allusion to the shape of the appendage of the forceps. 



Description of the species. 



1; P. m©destia, n. sp. % and 9 . — Fuscano-ochracea, thorace vittis 



subobsoletis, capite cano pollinoso, abdomine i'usco ; alls hyalinis im- 



maculatis. 

 Brownish-ochraceous, thorax with, indistinct stripes, head with a hoary 



bloom ; abdomen brown, wings hyaline, immaculate. Long. corp. 



0.17—0.18. 



Ground color of the head brown, entirely concealed above by 

 a thick hoary bloom ; rostrum somewhat paler ; palpi and antennas 

 brown. Thorax brownish-ochraceous, hardly shining above, in 

 consequence of a dull grayish dust; three pale brown, rather 

 indistinct stripes ; the intermediate one double ; stem of the 

 halteres pale, the knob brownish ; feet tawny, coxaa and basis of 

 the femora paler, tip of the tibiaa and the tarsi brown. Abdomen 

 brown ; genitals paler. Wings hyaline, immaculate ; veins brown. 



JSab. White Mountains, 1ST. H., June, 1864 ; five specimens. 



Gen. XL. RHAPHIDOLABIS. 



Two submarginal cells ; Jive posterior cells ; discal cell closed or open ; 

 the subcostal cross-vein is a considerable distance before the origin of the 

 second longitudinal vein ; the marginal cross-vein is very near the tip of 

 the first longitudinal vein (Tab. II, fig. 17, wing of R. tenuipes). Feet long, 

 slender ; tibiae with minute spurs at the tip ; empodia small, but distinct. 

 Eyes pubescent ; the front with a bump ; antennae 13-jointed. The forceps 

 of the male of R. tenuipes has long, needle-like, horny appendages. 



As I have taken some notes from a living specimen of R. tenui- 

 pes, I consider it as the type of the genus. In the following 



225. The name Astrolabis, which I gave it at that time, I give up as ob- 

 jectionable, and replace it by Plectromyia, a name I originally intended to 

 give to the genus now called Atarba. 



