14 2 DIPTERA OF NORTH AMERICA. [PART III. 



Wings of an unusual shape, on account of the great convexity 

 of the posterior margin, hyaline, with black veins and numerous, 

 partly only punctiform, partly rather large black spots of an 

 irregular shape ; the punctiform dots prevail in the middle, while 

 the borders of the wing are principally occupied by larger spots, 

 among which those along the posterior margin do not entirely 

 reach the latter. The peculiarities of the venation are indicated 

 above, among the generic characters. 



Hab. United States ; very common. 



Observation. — I do not entertain the slightest doubt that 

 Macquart's Platystoma annulipes is the above-described species. 

 His description agrees perfectly well, with the exception of the 

 words : " face blanche, une petite tache ronde d'un noir luisant de 

 chaque cote." All my specimens have, on the sides of the face, 

 or rather on the cheeks, nothing but brownish-black, opaque, 

 irregular spots. 



Gen. IV. IHYE1VIVIS R. Desv. 



Charact. — General appearance: Trypeta-like. 



Third antenna! joint oval ; cheeks broad, clypeus small, projecting 

 over the edge of the mouth. 



Wings narrow in comparison to their length, a little more attenuated 

 towards the apex ; the first longitudinal vein beset with bristles 

 upon the portion only, which forms the limit of the very long 

 stigma ; before this spot the first longitudinal vein appears almost 

 bare, the pubescence being, very short and delicate ; the two poste- 

 rior basal cells are comparatively large; the posterior angle of the 

 anal cell is pointed ; the posterior end of both crossveins is nearer 

 the apex of the wing than their anterior end, so that their position 

 is a very oblique one. 



The genus Myennis was established by Rob. Desvoidy for 

 Scatophaga fasciata Fab. As Trypeta scutellaris Wied. agrees 

 with that species in the above-enumerated characters, we can, for 

 the present, unhesitatingly refer it to Myermis. The peculiarity, 

 however, of the Pterocallina, of showing considerable plastic dif- 

 ferences almost from species to species, appears again in the two 

 above-named species. In P. scutellaris Wied. the eyes are less 

 round, the cheeks broader, the scutellum less swollen, the cross- 

 veins less approximated, the longitudinal veins, instead of straight, 

 somewhat undulated, and the third and fourth longitudinal veins, 

 towards their end, not distinctly convergent, but parallel. 



