102 DIPTERA OP NORTH AMERICA. [PART III. 



hardly crosses the fourth longitudinal vein posteriorly ; anteriorly 

 it extends as a rapidly contracting border along the costa as far 

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

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

 Hab. Washington, D. C. (Osten-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. 



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

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

 fovese. 



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



Wings cuneiform towards the basis, with 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 thoraceqne 

 interdum fuscis ; alas nigrse, fasciis hyalinis valde angustis secunda et 

 tertia arcuatis, hac ab alae apice late remote, vena transversa posterioi e 

 snbnormali. 



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 

 crossvein almost perpendicular. Lon<r. corp. 0.24—0.28 ; long. al. 

 0.21—0.23. 



Stn. Trypan flexa Wiedemann, Auss. Zweifi. II, p. 483, 11. 



Trypeia arcuata 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 



