PREFACE. 



IN the present work I have attempted to give a Monograph of 

 the North American Dolichopodidde. The geographical area em- 

 braced in it, as well as in my former Monographs on North Ameri- 

 can Diptera, is the same which has been adopted in Baron Osten- 

 Sacken's Catalogue, comprising Mexico and Cuba. I readily 

 acknowledge that by adopting such a wide area for the North 

 American fauna, we introduce many species which, properly 

 speaking, belong to a more southern fauna. But I was induced 

 to adopt this course as much by the circumstance that I possessed 

 many interesting species from Mexico and Cuba, as by the advan- 

 tage of conforming to the plan of the Catalogue of Osten-Sacken, 

 and thus affording a general view of the fauna pf a larger extent 

 of country. As the order of Diptera is remarkable for the wide 

 geographical range of the species, and as, for this reason, the 

 limitation of local faunas is more indefinite here than in most 

 other orders, the adoption of this somewhat arbitrary limitation 

 of the North American entomological area cannot present any- 

 thing objectionable. 



For the greatest part of the materials on which my work is 

 based, I am indebted to the liberal and disinterested assistance of 

 my esteemed friend Baron Osten-Sacken. Some very interesting 

 species were communicated to me by Mr. Le Baron, of Illinois. 

 The greater number of the species from Sitka was collected by 

 Mr. Sahlberg, and communicated to me for description by Pro- 

 fessor Maeklin in Helsingfors ; some species of the same region 

 are in the Museum of Berlin, and were obtained, if I am not 

 mistaken, also from Mr. Sahlberg. The study of the types of 

 Wicdemann's Collection, very liberally lent to me for examination 



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