116 DIPTERA OP NORTH AMERICA. [PART II. 



tinctly hairy. Hypopygium entirely disengaged, on a short pe- 

 duncle ; its exterior appendages lamelliform. The first joint of 

 the hind tarsi without bristles. First posterior cell narrow, 

 towards its end very narrow ; nevertheless the last segment of the 

 fourth longitudinal vein only very gradually approaches the third 

 longitudinal vein. 



The next related genera are Hercostomus and Hypophyllus ; 

 their species were formerly located with Sybistroma. From both 

 these genera Sybistroma differs, besides the peculiar structure of 

 the antennae of the male, by the very distinct hairs on the scutel- 

 lum. 



This genus was hitherto confined to the European Sybistroma 

 nodicornis, unless perhaps Sybistroma Dufourii belongs to it. 



The derivation of the name of this genus is not clear to me. 

 That it should be derived from <u$w*7, the spear, and crp^a, the 

 couch, is not probable, at least it would then be a very unsuccess- 

 ful composition. 



Gen. IX. HERCOSTOMUS. 



I have established the genus Hercostomus in the fifth number 

 of the " Neue Beitrage," upon the species Sybistroma cretifer 

 Ha\.,fulvicaudis Walk., and longiventris Loew. These species 

 agree in the following characters : in the distinct pubescence of 

 the otherwise plain arista ; in the structure of the proboscis ; in 

 the distinct hairs upon the surface of the suctorial flaps ; in the 

 glabrousness of the scutellum, and in the apparently sessile hy- 

 popygium of the male. The last of them approaches the species 

 of Hypophyllus very much, and shows some marked differences 

 from the two first, so that their consolidation into one genus may 

 be considered as provisional, and will certainly have to be modified 

 when a more considerable number of species will be known. 



In order to give more homogeneity to the genus Gymnopternus, 

 it was necessary, as I have remarked before, to exclude all those 

 species the third and fourth longitudinal veins of which are de- 

 cidedly convergent. These species, however, approach the above 

 named species of Hercostomus more than the species of any other 

 genus. I see no difficulty at present to unite them with the genus 

 Hercostomus, which is not ripe as yet for further subdivision on 

 account of the insufficiency of our knowledge of its species. 



