Preface 



Twenty-five years ago Williston's ^lanual of North American 

 Diptera (third edition), was offered to the public and in the interim 

 it has held the esteem of students of Dipterology in every quarter of 

 the globe. Williston's first synopses of families and genera appeared 

 in 1884 and following years in the Bulletin of the Brooklyn Entomo- 

 logical Society and in 1S88 the first edition of the ''Manual" appeared. 

 This "pamphlet", as it was modestly termed by its author, contained 

 88 pages, excluding as it did, the Nematocera and Muscoidea. The 

 second edition appeared in 1896, and included the Nematocera but 

 omitted the Tachinidaj and Dexiida^. The third edition contained all 

 the families, fifty-eight in number. 



The present attempt at a classification of the genera of North 

 American Diptera is the result of many years of study but it is incon- 

 ceivable that this work should be uninfluenced by such a masterpiece 

 as that of Williston. That a new synopsis is urgently needed Ijecomes 

 obvious when one considers the enormous number of new genera de- 

 scribed since the appearance of Williston's Manual, the realignment of 

 genera, the application of newly discovered characters and the increased 

 importance of the study of flies in relation to human welfare. 



Knowing, as I do, the excellent quality of Dr. Williston's work it 

 is with temerity that I offer this contribution to a critical public. Even 

 though great pains have been taken in its preparation and every effort 

 has been made to make the keys as complete and simple as possible I 

 fear that some few errors have crept in. That is inevitable. Where 

 they occur I do not know, nor do I offer excuses for them other than to 

 admit an utter ignorance in regard to the characters of thousands upon 

 thousands of Diptera, even though I have had available for study the 

 excellent collections of the Smithsonian Institution, Canadian National 

 Collection and the American Museum of Natural History and the gen- 

 erous assistance of various specialists. If mention is not made of those 

 who have contributed to this work, either wittingly or unwittingly 

 (through their synoptic revisions), it is only because the body of the 

 paper has increased to such proportions that a complete acknowledg- 

 ment must be omitted. 



A few innovations will be found. Where reasonably complete spe- 

 cific keys occur these are referred to in footnotes and the same is true 

 in' the case of family revisions. The synonymy has increased so greatly 

 that some indication of it must be given, especially where old familiar 

 names have been changed; this is indicated in the index and while it 

 is far from complete it is hoped that some help may be derived from 

 such an arrangement. 



