20 DIPTERA OF NORTH AMERICA. [PART II. 



marks which serve to distinguish one species from another. The 

 eighteen descriptions contained in the List of Diptera of the 

 British Museum mention at least occasionally such specific cha- 

 racters, and may therefore contain some data for identification; 

 but their great defect is that Mr. Walker has not given a complete 

 description of those peculiar marks which distinguish the males of 

 many species, so that, from his silence about these marks, one can- 

 not with safety conclude that they are "really wanting. This accu- 

 racy is absolutely necessary in order to make a description avail- 

 able. Among the forty-one North American Dolichopodid.de now 

 known to me, I recognize with certainty only a single species 

 already described before (besides the three species which North 

 America has in common with Europe, D. plumipes Scop., D. 

 brevipennis Meig., and D. discifer Stann.); it is the D. cuprinus 

 Wied. (= cupreus Say). This striking result induces me to 

 give a separate account of all the other species published by former 

 authors, in the order of their publication. 



1. obscurus Say. This species, also described by Wiedemaim, evi- 



dently belongs to the genus Gymnopternus and will be discussed 

 there. Wiedemann's collection affords no light upon this species. 

 It contains, it is true, two specimens of a Dulichopus marked obscurus, 

 but this is no other than a species of Tachytrechus, from the Cape^. 

 described by Wiedemann himself under the name of obsccenus. It 

 is probable that Wiedemann named this species, as he was in the 

 habit of doing, as soon as he received it in his collection, and that 

 when he described it afterwards, he changed its name to obsccenus, 

 on account of the already existing obscurus Say, neglecting, at the 

 same time, to change the etiquette in his collection. 



2. abdominalis Say. The abdomen is said to be reddish. If Say 



means a reddish, non-metallic color, then it is a distinct species, 

 entirely unknown to me, which will be easily recognizable even if it 

 is no true Dolickopus, as may very probably be the case. If, how- 

 ever, he means a metallic, coppery-red coloring, then the descrip- 

 tion is too unmeaning to pronounce even about its belonging to 

 Dolichopus in the restricted sense ; as to the identification of the 

 species, it is altogether out of question. 



3. groenlandicus Zett. A true Dolichopus with black as the prevailing 



color of its feet. It is not among the number of the species known 

 to me. 



4. heteroneurus Macq. is either a Pelastoneurus or a Paraclius. 



5. bifrons Walk. Dipt. Saund. It may be inferred, from the peculiar 



coloring of the face of this species, that it is a Pelastoneurus, 



