140 DIPTERA OF NORTH AMERICA. [PART U. 



pressed, its last segment narrow. The basal portion of the 

 entirely disengaged and inflected hypopygium forms a long 

 peduncle ; the outer appendages are rather filiform and whitish, 

 the inner appendages also. The last segment of the fourth longi- 

 tudinal vein with more or less flexure. 



The name of the genus (from avv, together, and attvos, narrow) 

 has reference to the very pointed shape of the third joint of the 

 antennae, which is peculiar to both sexes. 



Gen. XVIII. RHAPHIUM. 



The first joint of the antennae has no hairs on the upper side ; 

 the second is transverse ; the third glabrous, very narrow, in both 

 sexes very much elongated, though in the male more so than in 

 the female. Arista entirely apical, bare ; its first joint somewhat 

 elongated in the male. Scutellum glabrous. Hypopygium small, 

 rounded, rather imbedded ; its outer appendages more filiform than 

 lamelliform ; the inner appendages small ; the first joint of the 

 hind tarsi without bristles. 



The genus Rhaphium stands in next relation to the genera 

 Porphyrops and Xipliandrium. "With the species of Porphyrops 

 it shares the larger size, the greater number of bristles on the 

 feet, the broader wings, less narrow towards the basis. With the 

 species of Xiphandrium it has in common the great elongation 

 of the second joint of the antennas, the lesser density of hair on 

 the occiput, and the shorter hair upon the coxas and feet, also that 

 the last segment of the fourth longitudinal vein is less inflected. 

 From both these genera, however, Rhaphium is distinguished by 

 the somewhat longer first joint of the antenna?, which, particularly 

 in the male, is rather swollen ; by the great narrowness and the 

 glabrousness of the third joint, which is uncommonly elongated 

 not only in the male but also in the female ; by the glabrousness 

 of the arista, and finally, by the more n.arrow and more pointed 

 palpi of the female. The other genera most closely approaching 

 Ehaphium, as Systenus, Synarthrus and Smiliotus, cannot be 

 easily confounded with it, the hypopygium of the male in the spe- 

 cies of Systenus being very much pedunculated, the second joint 

 of the antennae in the species of Synarthrus reaching over the 

 third, and the abdomen in Smiliotus having only five segments. 



