168 Orthorrhapha brachycera. 



The species of Hercostomus occur chiefly in the same localities 

 as those of DolicJiopiis, on bushes and in low herbage on meadows 

 and in woods, at and near water, several species not rarely on water- 

 plants. Schiner says that many species may be seen sitting on the 

 surface of water; but some species are also found in more dry 

 locaUties on flowers, especially of Umbelliferæ. 



Of the genus about 60 species are known from the palæarctic 

 region; 15 have hitherto been found in Denmark. No doubt some 

 more species will still be found in our country, 



The genus Hercostomus was founded by Loew in 1857 (Neue 

 Beitr. V, 9); he created it for three species, and mentioned several 

 characters for it, especially the distinctly hairy arista and the bare 

 scutellum, the other characters mentioned being of less value; as the 

 type of the genus he gave longiventris. Already at the place cited 

 Loew speaks of a possible uniting of the genus with species of Gymnop- 

 ternus, and in 1861 (Neue Beitr. VIII, 26) he says that the species of 

 Gymnopternus with the narrowed first posterior cell are nearly related 

 to Hercostomus, and that the uniting of these species with Hercosto- 

 mus perhaps would give a better generic distinction between the two 

 genera; and again in 1864 (Mon. of Dipt. of North Am. II, 171, 76) 

 he says that the group of species with a narrowed first posterior cell 

 must necessarily be separated from Gymnopternus; finally in 1869 

 (Beschr. eur. Dipt. I, 278, Anm. 2) he divides Hercostomus and Gym- 

 nopternus after the mentioned character. This mode of distinction 

 has since been followed by many authors, among others Mik and 

 Kowarz, and is also used in the Kat. palåarkt. Dipt. The distinction 

 is however not valid ; thus in some species of Hercostomus (e. g. nigri- 

 pennis) the discal and cubital veins are only slightly converging; also 

 the characters from the hairiness of the arista and the scutellum are 

 impossible to use as a generic distinction, the scutellum is never 

 quite bare, but has in the species of Hercostomus some few hairs on 

 the disc and some at the margin. I have therefore here united the 

 two genera, but as there is in most species (Danish species) an obser- 

 vable difference, I have kept them as subgenera. 



Tahle of Subgenera. 



1. Cubital and discal veins more or less converging, 

 first posterior cell thus narrowed towards the end ; 

 scutellum almost bare, only with very few hairs, 

 chiefly at the margin; postocular bristles pale, or 

 {vivax and namts) black 1 . Subg. Hercostomus. 



