PREFACE. 



THE plan of the present publication is the same as that of Mels- 

 heimer's Catalogue of Coleoptera of the United States, revised by 

 Prof. Haldeman and Dr. Leconte, adopted by the Smithsonian 

 Institution, and published in 1853. 



It is intended to be merely a list of the species already described, 

 and not a synonymical catalogue ; that is to say, that among the 

 species enumerated, many may be synonyms, without being yet 

 known as such. In the present state of the knowledge of Ameri- 

 can diptera, the publication of a complete synonymical catalogue 

 is impossible ; but a list like the following, is an indispensable 

 preparatory work for the further study of that branch of Ento- 

 mology. 



This catalogue differs from Melsheimer's, in comprising not 

 only the species inhabiting the United States, but those of North 

 America in general, including Mexico, Central America, and the 

 West Indies. Many species described originally as belonging to 

 the last-named countries, may subsequently be found in the south- 

 ern parts of the United States. This extension of the plan of the 

 catalogue may therefore prove useful, in sometimes preventing a 

 species already described from being considered as new, when only 

 found for the first time within the United States. 



A further addition, by which this catalogue differs from Mels- 

 heimer's, will be found in the mention of the localities, where each 

 species has been discovered. This addition was the more neces- 

 sary, as the geographical limits of the catalogue had been ex- 

 tended. 



I have omitted all species marked simply "America," or those 

 of which the country was entirely unknown. 



