IO NORTH AMERICAN DIPTERA. 



he should not too hastily conclude that they are 'new'. 

 Until he has acquired a considerable acquaintance with 



different families, the work of classification may at times 

 be tedious, but by perseverance he can not fail to over- 

 come whatever obstacles families and genera may pre- 

 sent. He will be very much aided at the beginning by 

 having a tolerably large collection at his command with 

 which to make comparisons. Difficulties to the inexpe- 

 rienced will often disappear with positive evidence before 

 him, when negative characters would be doubtful. With 

 each genus in a family positively determined, the diffi- 

 culties and uncertainties of others will gradually disap- 

 pear. Better still if he -has numerous species reliably 

 named with which to begin his studies. The present 

 writer in his entomological career had few if any species 

 or genera determined for him by others, and he well ap- 

 preciates how wasteful of energies was such a method, 

 at the time unavoidable. For full generic descriptions 

 of many, perhaps the larger part, of the North American 

 genera, the student will find a most valuable aid in 

 Schiner's Fauna Austriaca, a work of which too much can 

 not be said in praise. The descriptions are remarkable 

 for their fullness, accuracy and simplicity, and, although 

 the work is forty years old, it has lost but little of its value. 

 To determine his species the student will need access 

 to a large number of books and papers, lists of which to 

 the present time will be found in Aldrich's admirable 

 and indispensable Catalogue of North American Diptera, 

 published by the Smithsonian Institution. One must 

 not, however, let the formidable lists frighten him. He 

 will not need them all to begin with, nor even the larger 

 part of them, and the earnest student can always be as- 

 sured of the sympathy and assistance of his fellow work- 

 ers. His earlier determinations, and those of the student 

 who is concerned chiefly in obtaining a broad general 



