322 DIPTERA OF NORTH AMERICA. [PART II. 



tinguish on account of their close resemblance ; in both, the same 

 frequence of species of Chrysotus, and not only the same variety 

 of plastic specific characters among them, but even a most strik- 

 ing conformity in the nature of these characters ; in both, nume- 

 rous species of Diaphorus and of forms related to them. A cer- 

 tain coincidence is even perceptible among those genera, which 

 hitherto are not represented either in the North American or in 

 the amber-fauna. It must be added, however, that the latter 

 shows nothing like the great abundance of the North American 

 fauna in species of genuine Dolichopus. 



It would be difficult at present to make any satisfactory state- 

 ment as to the relation in which the North American fauna of 

 Dolichopodidae stands to that of any other zoological province, as, 

 with the exception of the European fauna, our knowledge of other 

 faunas is not sufficient for this purpose. From what we know, 

 however, we distinctly perceive that the North American fauna 

 closely approaches the European and the North Asiatic faunae in 

 the species of the genera Hygroceleuthus, Dolichopus, Tachytre- 

 chus, Campsicnemus, Scellus, Hydrophones, Liancalus, Ghrysoti- 

 mus, and Xanthochlorus, whereas its coalescence with the South 

 American fauna is apparent in the species of Paraclius, Pelasto- 

 neurus, Lyroneurus, and Plagioneurus. The species of genuine 

 Gymnopternus, so numerous in North America, are but scantily 

 represented in Europe. The North American species of Diapho- 

 rus agree in part with the European, in part with the South 

 American species. The North American species of Argyra, Por~ 

 phyrops, Leucostola, and Liancalus do not show any striking 

 difference from the European species of these genera, but just as 

 little from the South American species. 



Of such species, as are common to Europe and North America, 

 the following have hitherto come under my observation : Doli- 

 chopus brevipennis Meig., Dolichopus plumipes Scop., Dolicho- 

 pus discifer Stann., Scellus spinimanus Zett., and Psilopus 

 pollens Wied. The first four of these species belong altogether 

 to specific types commoffly represented on both continents ; but 

 this is not the case with Psilopus pallens. This species unques- 

 tionably belongs to the circle of European types of Psilopus, 

 whereas all the North American Psilopus at present known 

 closely approach the types of their South American brethren. It 

 seems, therefore, not altogether unnatural to suppose that this 



