88 DIPTERA OF NORTH AMERICA. [PART III. 



only one which does not belong to the difficult group just char- 

 acterized ; it is distinguished from it not only by a different 

 picture of the wings, but also by some easily tangible plastic 

 differences. 



1st Group. Crossbands contiguous near the posterior margin. 



1. R. COnjlincta n. sp. 9 . — (Tab. VIII, f. 3.) Nigro-viridis, perlibus 

 praeter tarsorum basim nigris, tribus priinis alarum fasciis postice 

 cohserentibus. 



Blackish-green ; the feet, with the exception of the root of the tarsi, black ; 

 the first three crossbands of the wings contiguous posteriorly. Long, 

 corp. 0.16; long. al. 0.14. 



Blackish-green, shining. Front moderately broad, dusky fer- 

 ruginous-brown, almost black, laterally with a rather broad 

 border, pollinose with white. Antenna? reaching almost down 

 to the edge of the mouth, brick-red, except the third joint which 

 turns brownish or blackish towards its tip. Face and clypeus 

 metallic-black. Feet black ; the basis of the tarsi brick-red or 

 dirty reddish-yellow to a considerable extent. Halteres black. 

 Wings hyaline ; the four crossbands much broader than in the 

 following species, especially the first ; the second coalesces with 

 the first in the discal cell and the third unites with the first 

 near the posterior margin of the wing ; the band which forms a 

 border along the end of the anterior margin and the apex is 

 connected in the usual way with the third, at the anterior 

 margin. The small crossvein is but little beyond the middle of 

 the discal cell ; the second section of the fourth longitudinal 

 vein is strongly arcuated, and the posterior crossveins bisinuate. 



Eab. Maryland (Osten-Sacken). 



2d Group. Crossbands separated near the posterior margin. 



2. R. virid ula its R. Desv. % 9.— (Tab. VIII, f. 4.) Nigro-viridis, 

 interdum chalybescens, pedibus prater tarsorum basini nigris, primis 

 tribus alarum fasciis separatis. 



Blackish-green, sometimes more steel-blue ; feet, with the exception of 

 the root of the tarsi, black ; the first three crossbands of the wings iso- 

 lated from each other. Long. corp. 0.18 — 0.21 ; long. al. 0.15—0.2. 



Syn. Rivelha viridulans R. Desv. Myod. p. 729, 2. 

 Tri/peta quadrifasciata Harris, Cat. Ins. Mass. 



