228 NORTH AMERICAN TRYPETINA. 



bristly, on the under side with somewhat longer pile and 

 moreover from the basis to a little beyond the middle, with a 

 rather sparse row of long, almost bristle-like hairs ; hind tibiae 

 ciliated with rather weak bristlets. Tegulae almost as much 

 developed as in Hexachseta. Wings large, and, comparatively to 

 their length, less broad than in Hexachseta ; the venation, with 

 the exception of the difference in the course of the fourth vein, 

 already adverted to, is very like that of Hexachseta, only all the 

 cells, and especially the stigma, are longer in comparison to their 

 breadth ; the posterior angle of the anal cell is drawn out in an 

 equally long and pointed lobe ; the whole of the first longitudinal 

 vein and the third some distance beyond the small crossvein, 

 are bristly. The very characteristic picture of the wings in 

 Acrotoxa is sufficiently rendered by the figures 5 and 6 of Tab. 

 X, and 19-27 of Tab. XI. The portions of this picture which 

 could not well be called bands (fasciae), or stripes (vittee), I 

 have called rivulets (following in this Meigen's example, who 

 called them rivuli in latin, and Bache in german). The same 

 term may be applied to the species of Acidia. The species of 

 Acrotoxa are often very much alike, and very difficult to dis- 

 tinguish in the male sex ; the females are frequently easier to 

 distinguish on account of the very different length of the oviposi- 

 tor in different species. 



Observation 3. — In view of the difficulty of this group and of 

 the probable occurrence of species belonging to it in some por- 

 tions of the North American continent and of the West Indies 

 (besides Trypeta fraterculus Wied., already referred to), I 

 deem it useful to enter into a more detailed examination of them. 

 Most of the numerous Acrotoxse occurring in the European 

 museums come from Brazil, and pass rather indiscriminately for 

 the Dacus parallelus Wied. I will give a description of this 

 species, based upon the original specimens in the Wiedemann- 

 Winthem and the Seckenberg collections, and of some of the 

 species more closely allied to it, confining myself to those species 

 only which are known in both sexes. Special mentions of color- 

 ing and picture will be omitted, as the former is clay-yellow in 

 all the species, and the latter very probably is pretty much like 

 that of T. ludens, as given above, at least in living specimens ; 

 in drying it becomes somewhat indistinct, and affords no trust- 

 worthy marks for discrimination. 



