56 DIPTERA OF NORTH AMERICA. 



frequently the case with the base, or a greater part, or even the 

 whole length of the third longitudinal vein ; much more seldom 

 there are bristles on the fifth longitudinal vein. The two small 

 basal cells are proportionately large; the posterior of them, i. e., 

 the anal cell in most, but not all species, has its posterior angle 

 drawn out into a point. The thickening of the costal vein always 

 reaches to the fourth longitudinal vein. The surface of the wing 

 has in all species a microscopic pubescence. 



From the above enumerated structural peculiarities we may de- 

 rive the following characters for the family of Trypetidce: 



1. The borer of the female is corneous, three-jointed, and ends in 



a simple point ; the penis of the male answers the borer in 

 length, and is thread-like and not divided at its end. 



2. The front is broad in both sexes, and there are stout bristles on 



the anterior part of its lateral border, not belonging to the 

 row which descends from the vertex, but forming a separate 

 row which is placed nearer to the lateral border of the front. 



3. There are spurs at the end of the middle tibiae, and no bristles 



whatever on all tibiae, except, in a few- species, bristle-like 

 hairs on the upper side of the posterior tibiae. 



4. The neuration is the completes! among the Acalyptera\ the 



auxiliary vein takes a steep turn towards the border of the 

 wing, and becomes indistinct towards its end. 



4. On the relations of this family. 



The family most nearly related to the Trypetidce is that of the 

 OrtcdidcB. The two principal characters, by which the former are 

 distinguished from the latter, are the stout bristles existing on the 

 anterior part of the lateral border of the front, and the steep direc- 

 tion in which the tapering end of the auxiliary vein runs to the 

 border of the wing. Both these characters are very constant; 

 should it happen that one of them is less sharply expressed, the 

 other will be the more striking, and so an absolute certainty is 

 afforded about the limits of these two families, the species of which 

 have hitherto been so much mixed together. 



The PallopteridcB and Lonchceidce are not quite so nearly related 

 to the Trypetidce as the Ortalidce. They also want the bristles 

 on the anterior part of the lateral border of the front, and the 

 end of the auxiliary vein never shows the peculiarity which cha- 



