2 DIPTERA OF NORTH AMERICA. [PART III. 



Through the successive, although disconnected, publications 

 of several authors the systematic arrangement of the Ortalidse, 

 like that of some other families of diptera, has gradually reached 

 a state of confusion which it is impossible to unravel without a 

 detailed and somewhat lengthy discussion. I may be excused, 

 therefore, if I preface the description of a comparatively small 

 number of American species by an unusually long introductory 

 chapter. 



In order to point out the relationship of the Ortalidse with 

 other families, as well as the differences which distinguish them, 

 it is necessary, first of all, to discover those characters which 

 serve to define the family. 



The European Ortalidse. 



The examination of the works of Meigen, the founder of 

 systematic dipterology, will afford a solid basis to proceed from, 

 and I will begin with the European species which are the longest 

 known and the best investigated. 



Meigen's Genus Ortalis. 



The nucleus of the European Ortalidse is formed of those 

 species which Meigen has brought together in the genus Ortalis, 

 a genus which, in his acceptation, far exceeded the limits which 

 we are accustomed to give to genera at present. ^ 



1. Characters which Meigen's species of Ortalis have in 

 common. 



I discovered a number of characters which the species of 

 this genus have in common, and which also occur in many 

 species added to the genus by subsequent authors. These com- 

 mon characters, to the exclusion of those which also belong to 

 most of the neighboring families, are the following : — 



Front broad in both sexes ; a more or less distinctly developed 

 small callosity runs from each corner of the vertex down the 

 front ; it bears in front of the lateral bristle of the vertex one 

 or two distinct additional bristles ; beyond this, the front is beset 

 with only short hairs, or else quite bare ; it never has the second 

 row of bristles, nearer the orbit, which distinguishes all the 

 genera of Trypetidse. 



Eyes bare, even under a strong lens; the compound micro- 

 scope shows only some sparse, very short hairs. 



