PREFACE. VII 



faniil}- in monographs. It will be a long time of, course, before 

 this last stage is reached in all the families of North American 

 diptera, and for this reason, this new Catalogue, which represents 

 the achial state of our knowledge of these diptera, is not entirely 

 homogeneous; a portion of it only is synonymical and critical, 

 and the rest is still a mere list of names, a compilation. The 

 Catalogue may, in this respect, be divided into three groups of 

 families , representing three stages of our knowledge of the 

 species enumerated: 



1. The families of the first group have been worked out 

 in monographs, containing comparative descriptions of all -the 

 species (as far of course, as represented in the collections), with 

 analytical tables, or else with figures, to facilitate identification. 

 Such families are the Boliclwpodklae , Ortalidae and Trypetklae 

 (monographed by Dr. Loew) ; the Tiimlidae hrevij^aljoi and 

 Tahanklac (monographed by myself). The beginning of a similar 

 work was made by Mr. Loew for the Ephydrinidae and Sciomy- 

 zklac and by me for the genus Syrp>lius. 



2. In the families of the second group , collections have 

 been formed, a certain number of earlier descriptions have been 

 identified and synonymies made out; many new species were 

 described; but a monographic treatment is still wanting. Such 

 families are the Asilidae (with the exception of the section 

 Astlina) , the Bomhylklae, Syrphklae, T'qndidae longipcdpi] also 

 the Enipidac, M'tdaidae, Cyrtklae, Bihionidac, Mycctopliilklae 

 and a number of the smaller families among the Miisckkie 

 acalypterac. 



3. In the families of the third group, collections have been 

 formed, but they are, for tlie most part, not named. The 

 Catalogue, in such families, is a mere compilation of references 

 to descriptions by earlier writers. Such families are : the 

 Cidicidae, Chironomidae, Conopidae, the whole group of Muscidae 

 ccdypterae and the section AsiVvna. 



Collection of type-specimens. A difference between the old 

 and the new Catalogue, perhaps more important than that already 

 explained, consists in the fact, that the majority of the species 



