138 Annals Entomological Society of America [Vol.11, 



In his Manual Williston says that ' ' In general the subdivisions 

 of the old genus Asilus are very vague and hard to define, and 

 many of them are doubtfully entitled to recognition. At the 

 most, few, if any, of them are based upon real generic characters 

 and the names are only useful as aids in the determination of 

 the numerous forms." 



Lundbeck, in his Diptera Danica 1908, II, 53, gives what argu- 

 ment there is for the other side when he says of these names that 

 "Though it cannot be denied that as genera they are far more 

 closely allied and taken in a narrower sense than genera are com- 

 monly, I shall yet retain them, chiefly because they are 

 generally in use and at all events give valuable hints about the 

 natural classification of the species." 



Before beginning the study of the species considered in this 

 paper, I procured representative specimens of Loew's groups 

 from Europe by exchanging with Dr. M. Bezzi and others, and 

 with these for reference have undertaken to place the North 

 American species. The list offered below indicates the success 

 achieved, but as may be noted some of the species do not fall 

 naturally into any of the groups and even in some cases where a 

 decision appears to have been reached, there are difficulties in the 

 way of a perfectly satisfactory conclusion. It may be mentioned 

 also that Dr. Bezzi encountered some difficulty in placing the 

 Nearctic species, for at the end of the Asilinae in the recent Cata- 

 logue of Palearctic Diptera is a list of no less than twenty-nine 

 species, which from the evidence cannot be placed in the so-called 

 genera, but are given as falling under the genus Asilus in the wide 

 sense. 



By giving only Asilus generic rank and using the other names, 

 that often have been considered as genera, simply as names of 

 groups, some questions in priority come up for solution. Since 

 Europeans were the first to arrange their species in reference to 

 Loew's classification, the proper procedure would be for them to 

 be the first to discard it. As it is students in America have 

 described many of their species on the ground that Loew's names 

 were valid generic terms, using the same specific name in two or 

 more genera. If these names are considered as genera in Europe, 

 as is the case in the recent catalogue mentioned above, and only 

 as groups of one genus in America, a student in the latter country 

 hardly knows what is the proper disposition of the synonymy 

 question in his fauna. With these facts confronting me, I do 



