10 THOMAS SAY FOUNDATION 



hairy first vein, taking helicis as type. While I have 

 found no case of inconstancy of this character in the 

 North American species, such are said to exist in 

 Europe ; and at the hest this character cuts across the 

 others which seem to have subgeneric or even group 

 value, in such a way that it is clearly unavailable for 

 generic separation in Sarcophaga. This has been rec- 

 ognized by several dipterists. 



A survey of the present status of the Muscoid 

 Diptera indicates unmistabably that our great need 

 is not more genera, but a more complete knowledge 

 of species. The tendency of extreme generic special- 

 ization is to erect about itself impenetrable barriers of 

 names, as is well illustrated by Desvoidy and Brauer. 

 Genera conceived in this mental atmosphere are likely 

 to be almost wholly subjective creations, which make 

 no impression on the minds of others. The argument 

 that the classification must express the relations has 

 its dangers, partly from the subjective elements in- 

 volved, and partly from the fact that the classification 

 has also another important function, — to provide us 

 with names for our species, which should be as stable 

 as possible if they are to have any usefulness. Furth- 

 ermore, to separate a species from the genus in which 

 it has been located expresses one relation, that of dif- 

 ference ; but it obscures another, that of resemblance, 

 which may be more important. One of the main ob- 

 jects of the present work is to make the identification 

 of species as simple and certain as possible, and thus 

 to attract biological and economic workers into the 

 group. This object would inevitably be defeated by 

 the erection of a considerable number of indistinctly 

 separated genera. These are the governing consid- 

 erations which have prompted the preservation as 

 nearly as practicable of the old genus Sarcophaga. 

 Spfcial Taxonomic Characters. 



It is assumed that entomologists using the pres- 

 ent paper will be tolerably familiar with terms used 

 in describing Diptera; the papers of Parker and 

 Bottcher, and Williston's widely used Manual of 



