169 



XII. A List of the Leptidae, Mydaidae and 

 Dasypogonina of North America 



BY CH. R. OSTEN SACKEN. 

 [Read before this Society, Oct. 10, 1874.] 



OwiifG to the large increase in the number of the described 

 species of North American Diptera since the publication of my 

 "Catalogue" (Washington, Smithsonian Institution, 1858), a new 

 catalogue of the same kind becomes a matter of necessity. I will 

 endeavor to prej^are such a work, not exactly on the same plan with 

 the former, but with the improvements required by the present state 

 of the science. Instead of merely compilatory, the new catalogue 

 will be synonymical, at least as far as our present knowledge ad- 

 mits of it. 



Of course, I could not attempt such a publication with much 

 hope of success, without the prospect of the assistance of my friend 

 and valued correspondent, Dr. Loew. The labor he has devoted for 

 the last fifteen years to the study of American Diptera, places him 

 at the head of those who know anything about this branch of the 

 American fauna. On his assistance I have drawn, and mean to 

 draw largely during my work. 



The geographical area of the new catalogue will be the same as 

 that of the old one. That is, it will embrace the North American 

 Continent as far as the Isthmus of Panama. But in order to facil- 

 itate the survey of the species found within the United States, I 

 intend to arrange the species of each genus in three groups, the 

 first of which Avill embrace the Atlantic States, the second the 

 Pacific States, and the third the tropical countries (Mexico, Central 

 America and the West Indies). For the dividing line between the 

 Atlantic and Pacific provinces, I take the line of the water-shed of 

 the two Oceans. A species belonging to two groups simuUaneously 

 will be placed in the earlier group. Within each group the species 

 Avill be arranged alphabetically, 



BUL. BUF. SOC. NAT. SCI. (^21 OCTOBER. 187 J. 



