170 DIPTERA OF NORTH AMERICA. [PART II. 



characters which distinguish Lyroneurus from Diaphorus. The 

 last of these characters is decisive for the maintenance of the 

 genus Lyroneurus, as the elongation of the pulvilli of the fore 

 tarsi in the male cannot be dispensed with in the character of the 

 genus Diaphorus, without rendering the limit between Diaphorus 

 and Ghrysotus entirely uncertain. 



The genus Lyroneurus, to which also belongs D. adustus 

 Wied., seems to contain only American species; they appear to 

 be particularly numerous in South America. 



The name of the genus (from jtwpa, the lyre, and vtipov, the 

 nerve) has reference to the lyre-shaped space between the third 

 and fourth longitudinal veins. 



1. L. caei'Mlescens Loew. % . — Viridis, thorace et abdominis dorso 

 cseruleis, femorum apice tibiisque totis testaceis, tarsis ex nigro fuscis. 



Green, thorax and dorsum of the abdomen sky-blue ; tip of the femora and 

 the whole tibise brownish-yellow ; tarsi black-brown. Long. corp. 0.22. 

 Long. al. 0.25. 



Syn. Lyroneurus cserulescens Loew, Wieu. Ent. Mon. I, 39. — Loew, Neue 

 Beitr. VIII, 60. 1. 



Light metallic-green, most of the upper side of the thorax, of 

 the scutellum and the greater part of the upper side of the abdo- 

 men sky-blue or violet. Face of considerable and uniform breadth 

 and so thickly covered with gray-whitish dust that no trace of the 

 blue-green ground-color is left. Palpi black, with white-gray 

 dust and with strong black hairs. Antennas black, short. Front 

 of uniform breadth, equal to that of the face ; the dust upon it is 

 so thick that hardly a trace of the ground color is left. Cilia of 

 the upper orbit black, cilia on the lateral and inferior orbits white 

 and forming a rather thick beard. Thorax pale green, upon the 

 middle line and upon the whole hind part sky-blue, or shifting to 

 violet. The rather thick dust on the upper side of the thorax has 

 a gray-brownish tinge. Scutellum blue or violet with gray-brown 

 dust, on each side with a stronger and with a weaker bristle, on 

 the surface bare. Pleurae green with rather thick gray- white 

 dust. Abdomen cylindrical, metallic-green ; its upper side 

 shining blue or violet from the middle of the second segment to 

 the tip. The hair upon the abdomen is black ; the bristles on the 

 hind margin of the single segments are but of moderate lensrth. 



