REMARKS ON THE GENERIC CHARACTERS, 



EXPLANATORY TO THE PLATES. 



Although the present publication on North American Dolichopodidae was 

 based upon a considerable number of species, it can be safely assumed 

 that these species do not represent all the Genera occurring in North 

 America. I have, therefore, added the characters of even those genera of 

 the family, representative species of which have not yet been found on 

 that contiuent, and I hope that this addition will prove useful to those 

 desirous of studying this family in detail. In order to facilitate the recog- 

 nition of generic characters, five plates, drawn for this purpose, have been 

 added to this volume. But as on these plates every genus is represented 

 only by a single species, this might easily give rise to the mistake that 

 specific marks belonging to that particular species are generic characters. 

 In order to prevent this, I have deemed it advisable to append to the plates 

 the following explanatory remarks on the generic characters, which should 

 always be consulted in determining species. 



The figures of the antennae show that the "first joint in No. 1 — 16 is dis- 

 tinctly provided with bristles on the upper side ; in No. 17 — 44, on the con- 

 trary, it is glabrous. This distinguishes the two principal divisions of the 

 Dolichopodidae. 



Among the species belonging to the FIRST PRINCIPAL DIVI- 

 SION the genera numbered from 1 to 12' have a completely disengaged, 

 elongated hypopygium ; those numbered 14—16 a small, rounded, more or 

 less imbedded one ; in No. 15 the hypopygium is short and sessile, but not 

 imbedded, so that this genus (Diostracus) forms a transition from one of 

 these two subdivisions to the other, and may be included either in the first 

 or in the second. I have given preference to the first arrangement, but 

 have separated this genus from all the others of this subdivision on 

 account of the very large size of the palpi of the male. 



The other genera of the First Sub-division stand much nearer to each 

 other in their organization ; they may, however, be easily arranged into two 

 groups according to the circumstance whether the first joint of the hind 

 tarsi is provided with bristles on its upper side (No. 1 — 3), or is without 

 such bristles (4 — 16). To the first of these groups belong: Hygroceleuthus 

 (1), Dolichopus (2), and Rhagoneurus (3). The difference between 



1 These numbers refer to the plates. 



(345) 



