PELASTONEURUS. 103 



Gen. V. PELASTO.VEIBUS. 



The characters of the genus are the following : First joint of 

 the antenna? short, hairy on the upper side; third joint rounded ; 

 arista dorsal, distinctly feathered. Face in both sexes compara- 

 tively broad, upon its lower part strongly convex; its lower 

 margin is sharp, and forms a curve. Proboscis stouter than in 

 Gymnoptemus, and approaching in its structure the species of 

 Medeterus. The first joint of the hind tarsi without bristles. 

 The last segment of the fourth longitudinal vein turns forward at 

 or beyond its middle in a strong curve, and runs then almost in a 

 straight line towards the margin of the wing, which it reaches 

 closely in the vicinity of the tip of the third longitudinal vein, so 

 that the first posterior cell is almost closed. The hypopygium 

 is entirely disengaged, very much elongated, pedunculated, with 

 lamelliform black appendages, which, in most of the species, have 

 a very elongated form, and are of a more solid substance than in 

 the allied genera. 



The next related genus is Paraclius. The differences of both 

 have already been detailed above. Pelastoneurus can hardly be 

 mistaken for any other genus. 



As yet, only American species of Pelastoneurus have been 

 made known. Among the species described by former authors, 

 Dolichopus maculipes Walk., and D. bifrons Walk., seem to be- 

 long here. The name of the genus (from nt-Ku^, I approach, and 

 vivpov, the nerve) has reference to the position and the peculiar 

 course of the last segment of the fourth longitudinal vein. 



Table for the determination of the Species. 



. ( Cilia of the inferior orbit black. 2 



( Cilia of the inferior orbit pale. 4 



{Thorax with a large spot of white dust on the posterior margin. 

 1 longicauda Lto. 

 Thorax without a spot of white dust on the posterior margin. 3 



o ( Wings blackened. 2 lugubris /.»■. 



I Wings gray. 3 laetus /.»•. 



. ( Fore coxjb blackened at the basis. 4 vagans /.»-. 



( Fore coxa; not blackened at the basis. 6 cognatus /.»-. 



