PREFACE. IX 



cipal dipterological writer in Europe and that the study of his 

 papers cannot enough be recommended. 



SYSTEM. The systematic distribution of the diptera and the 

 natural affinities of some of the larger and smaller groups, are 

 still matters of uncertainty. I have preserved, with slight modi- 

 fications, the arrangement adopted by the most recent writers. 

 It has the advantage of adapting, as much as possible, the 

 division in Ortliorliaplia and Cyclorliaplia, to the sequence of the 

 families , as found in Meigen and other early writers. The 

 Xylophagidae , Stratiomyiclae , Coenomyidae , Acanthomeridae, 

 Tabanidae and Leptidae seem to form a natural group, within 

 which it is impossible to bring about a satisfactory linear ar- 

 rangement. I placed the Asilidae between this group and the 

 Bombylidae, in order to bring together the families provided 

 with a posterior intercalary vein. But I am not at all sure 

 whether this is not a character of secondary importance , and 

 whether Dr. Schiner was not right in placing the Bombylidae 

 nearer to the Tabanidae. The relationship of the Blepharoceridae, 

 Psychodidae, Cyrtidae and Therevidae is likewise uncertain. 

 Orplmephila and Dixa are altogether incertae scdis. 



Although I consider the Aplianqitcra as directly related to 

 the Mycctopltflidae , I have omitted them from my list, because 

 they have hitherto formed a separate object of study. 



GEOGRAPHICAL RANGE. The region, embraced in the present 

 Catalogue is the same as that of its predecessor: all North 

 America, north of the Isthmus of Panama, including the West- 

 Indies. But, instead of enumerating the species promiscuously, 

 as it was done in the earlier Catalogue, I have, within each 

 genus, separated the species occurring north of the Mexican 



Record was prepared by Erichson from 1838 to 1847; by Schaum from 

 1848 to 1852; by Gerstaecker from 1853 to 1866; by Brauer from 1867 

 to 1870; and by Bertkau since that year. In England, the Zoological 

 Record, published yearly since 1864, also contains an admirably prepared 

 review of entomological publications. The frequent perusal of these 

 Records cannot enough be recommended to those who wish to become 

 thoroughly acquainted with the literature of any branch of entomology. 



