ORTALID.E — RIVELLIA. 87 



markably narrow; the small crossvein is in the middle of the 

 discal cell; the posterior angle of the anal cell is rounded and 

 the last section of the fourth longitudinal vein is parallel to .the 

 third. 



Bab. Cuba (Gundlach). 



Gen. III. RIVELLIA R. Desv. 



Charact. — Front of equal breadth, not projecting in profile. 



Antennae usually reaching down to the margin of the mouth; third 

 joint long and narrow ; arista with a very short pubescence. 



Face rather excavated, its lower part projecting ; the lateral portions 

 very narrow ; clypeus broad ; occiput moderately turgid ; eyes 

 high ; cheeks moderately broad. 



Scutellum convex, with four bristles. 



Wings: Marginal and submarginal cells comparatively broad; the 

 second section of the fourth longitudinal vein remarkably sinuate, 

 with the convexity encroaching upon the discal cell, so that the 

 latter appears much narrower before the small crossvein than behind 

 it ; the last section of the fourtli longitudinal vein is parallel to the 

 third vein or very slightly diverging ; posterior angle of the anal 

 cell rounded. 



A large number of closely resembling species belong to this 

 genus; the picture of the wings of most of them is nearly the 

 same, so that this picture alone helps to recognize the species 

 belonging here; it consists of four brown or blackish-brown 

 crossbands; the first starts from the root of the wing and is the 

 most oblique of all and the shortest; the second, somewhat 

 longer and less oblique, runs over the small crossvein; the third, 

 which covers the posterior crossvein, is perpendicular and reaches 

 from the anterior to the posterior margin of the wing; the fourth 

 starts from the anterior margin, near the origin of the third band, 

 and forms a border along the apex of the wing. The North 

 American fauna seems to abound in these species. The appa- 

 rently total absence of plastic differences between them and the, 

 as it seems, not unimportant variation in the coloring of some of 

 them, render their separation very difficult, especially when there 

 are only single specimens for comparison. I hope not to have 

 gone amiss in the definition of those which I know. Whether 

 I was mistaken or not, those may judge who have the opportuni'y 

 of observing these species in life. 



Among the species described below, Bivellia conjuncta is the 



