420 CATALOGUE OF NORTH AMERICAN DIPTERA. 



genera and species, which I have endeavored to distribute in accordance with 

 the classification in the work mentioned. I cannot hope to have made a perfect 

 success of this, considering the difficulty of the family. 



The work of Brauer and Bergenstamm, Vorarbeiten zu einer Monographic 

 der ]iluscaria schizometopa, forming parts iv, v and vi of the series called 

 Zweifliigler des Kaiserlichen }iluseums zu Wien, is an elaborate and extensive 

 work, characterized by a minute subdivision of the group into numerous so- 

 called families, sections, super-genera, and genera. Although it shows an im- 

 mense amount of patient and faithful study, it is vitiated by a failure to grasp 

 the natural divisions between groups of the same category. Hence it must be 

 used with caution, and much experience is necessary before one can judge of 

 its authoritativeness in a particular case. The table contains many illusory 

 characters, and the usefulness of the work is further marred by a succession of 

 addenda, modifying the system in numerous parts, and making it still more 

 difficult to follow. 



The work of Townsend shows itself to have been powerfully influenced by 

 the one just mentioned; hence there is a serious confusion of genera, and in 

 some instances the same species is described several times under different gen- 

 era, or in the same genus. The worst instance of this will be found under 

 Myiophasia ccnca. This was not the result of carelessness but of a too 

 narrow splitting up of genera and species, in the attempt to follow Brauer and 

 Bergenstamm. The specific descriptions of Townsend are conscientious and 

 faithful, and among the most recognizable of any in the family. 



The extensive article by Van der ^^'ulp on the Mexican and Central Ameri- 

 can fauna, published in vol. ii of the Diptera in Biologia Centrali-americana, 

 goes to the other extreme in the matter of genera, and the large genera in it 

 are without exception heterogeneous collections, which can at present hardly 

 be placed consistently in the system here adopted. 



The descriptions by Bigot are in every way objectionable, almost always re- 

 ferred to the wrong genus, and seldom containing the essential data. Most 

 fortunately, the types of nearly all the species have been examined by Brauer, 

 who has elucidated them in accordance with his system in three articles in 

 Sitzungsberichten der Kaiserlichen Akademie der Wissenschaften (Mathemat- 

 ischen-Naturwissenschaftlichen Classe, Bd. cvi, cvii and cvin). This makes it 

 possible to arrange them fairly well in the present work. 



The following tables of genera may be consulted : 



Townsend, Proc. Ent. Soc. Wash., ii, 92, 96; Trans. Amer. Ent. Soc, 



XIX, 134. 

 Van der Wulp, Biologia, Dipt., 11, 5 and 41. 

 CoQUiLLETT, Revision Tach., 30 ; this is most important. 

 The S3-nonymy adopted by Coquillett in his Revision has been followed' rather 

 closely for the species included in that work, without giving credit in the ref- 

 erences. 



To facilitate reference through the index, I mention the following cases where 

 the genus might not otherwise be found : 



Argyrophylax rostrata CoQ. has been placed in Siphostiirmia. 



Ceromasia Rond. is a synonym of Masicera; but only chrysocephala and zonata 

 of Bigot have been placed there. His abhrcviata, pictigaster, qitadrivittata and 

 spinipes will be found in Hyposfcna, while his castanifrons has been referred to 

 Prosplierysa. 



Chaetolyga is a synonym of Winthcmia; but the species of Bigot will be 

 found under Exorisfa, Hyposfcna, Phoroccra and Winthemia. 



