104 DIPTERA OP NORTH AMERICA. [PART II. 



Systematic arrangement of the Species. 



I. Cilia of the inferior orbit black. 



1. longicauda Lw. 3. laetus Lw. 



2. lugubris Lw: 



II. Cilia of the inferior orbit pale. 



4. vagans Lw. 5. cognatus Lw. 



Description of the Species. 

 I. ClLIA OP THE INFERIOR ORBIT BLACK. 



1. P. longicauda LOEW. . Aeneo-niger, facie argenteo micante, 

 sub anteunis triangulum nigrum gerente, ciliis oculorum inferioribus 

 nigris. 



Bronze-black ; face with a silvery lustre, with a black triangular spot 

 under the antennae; cilia of the inferior orbit black. Long. corp. 0.17. 

 Long. al. 0.16. 



SYN. Pelastoneurus longicauda LOEW, Neue Beitr. VIII, 37, 1. 



Face, for a $ , extremely broad, the inferior two thirds of it are 

 strongly convex and have a bright silvery-white reflection, which 

 shows a somewhat olive-brown appearance only in a certain ob- 

 lique light ; the upper, flat portion of the face has in each lower 

 corner a deep, triangular spot with a silvery lustre ; that triangu- 

 lar part of it, which is not covered by this spot, appears deep- 

 black, when seen from above ; seen from below, it appears less 

 dark and somewhat dusty. The lower margin of the face is very 

 sharp. Palpi large, on the outside with a silvery-white lustre 

 and covered with black hairs. Front shining blackish. Antennae 

 brownish black ; the under side of the first and second joints 

 brownish-red ; the rounded third joint rather large. Arista 

 rather short, very much thinner towards the tip, and upon the last 

 two thirds feathered with short hairs. Cilia of the inferior orbit 

 black. Thorax bronze-black, rather shining, with an almost imper- 

 ceptible white dust ; the upper side of the thorax shows five spots 

 covered with snow-white dust, namely one on each side near the 

 transverse suture, one in the shape of a dot, on each side above 

 the root of the wing near the posterior corner, and finally a large 

 triangular spot in the middle of the hind margin ; the velvet-black 

 stripe-like double spot immediately above the root of the wing, 

 so common in the species of this genus, is very distinct here. 



