ADVERTISEMENT. 



The present publication is Part III of a work upon the Dip- 

 tera of North America, prepared at the request of the Smith- 

 sonian Institution, by Dr. H. Loew, of Guben, Prussia, well 

 known as one of the most eminent cultivators of this branch of 

 entomology. 



The first part of this series of monographs was published in 

 18G2, and included the families of Trypetidse, Sciomyzidee, 

 Ephydrinidse, and Cecidomyidse. The second part appeared in 

 18G4, and consisted principally of a monograph of the Dolicho- 

 podidse. The fourth part was issued in 1869, embracing a 

 monograph of part of the Tipididae. 



They were not published in sequence, but in the order in 

 which materials could be collected for their preparation. The 

 original manuscript of Dr. Loew was written in German, and 

 the Institution is indebted to Baron II. Osten-Sacken for trans- 

 lating it into English; and to Mr. R. A. Witthaus, Jr., of New 

 York, for revising and correcting the proof-sheets, in the absence 

 of Baron Osten-Sacken. 



JOSEPH HENRY, 



Secretary S. I. 

 Washington, Dec. 1873. 



l'HILADELPHTA : 

 COLLINS, PRINTER. 



