102 DIPTERA OF NORTH AMERICA. [PART III. 



hardly crosses the fourth longitudinal vein posteriorly; anteriorly 

 it extends as a rapidly contracting border along the costa as fat- 

 as the end of the second longitudinal vein, so that it has rather 

 the shape of an apical spot than of an apical border. 

 Hah. Washington, D. C. (Osteu-Sacken.) 



Third Section : Cephalina. 



Gen. I. TRITOXA nov. gen. 



Charact. — Body slender ; abdomen narrow at the basis ; feet rather long, 

 front tibiae before the end of the upper side with a stronger bristlet. 

 Hairs and bristles rather short ; thoracic dorsum with bristles 

 along the sides and upon its posterior margin only. 



Antenna long and narrow ; the second joint short ; arista with short 

 hairs. Face almost shield-shaped, with rather indistiuct antennal 

 fovex'. 



Palpi very broad; proboscis rather stout, mentum but little inflated. 



Wings cuneiform towards the basis, wit'.i a very narrow alula; second 

 longitudinal vein not conspicuously arcuated ; third and fourth 

 irregular in their course, which causes the anterior basal cell to 

 expand before its end ; first longitudinal vein beset with bristles 

 upon the greater portion of its course ; crossveins approximated to 

 each other. 



This genus contains reddish-brown and black species, with 

 dark wings, marked with three hyaline, oblique, more or less 

 arcuated crossbands. 



1. T. flexa Wied. % 9 . — (Tab. VIII, f. 10.) Nigra, capite thoraceque 

 interdum fuscis ; alse nigrae, fasciis hyalinis valde augustis secunda et 

 tertia arcuatis, hac ab alae apice late remota, vena transversa posteriore 

 eubnormali. 



Black, head and thorax sometimes brown ; the wings black, with three 

 very narrow hyaline bands, the second and third of which are arcu- 

 ated ; the latter is rather remote from the apex of the wing; posterior 

 crossveiri almost perpendicular. Long. corp. 0.24—0.28 ; long. al. 

 0.21—0.23. 



Syn. Tryp'ta flexa Wiedemann, Auss. Zweifl. II, p. 483, 11. 



Tn/peta arcnata Walker, Ins. Saunders, p. 383. Tab. VIII, f. 3. 



Fully colored specimens are altogether deep black; in very 

 pale specimens, on the contrary, the whole head, the thorax, and 

 the feet, the latter usually with the exception of the upper side 

 of the femora, are often brown ; vestiges of this color frequently 



