ADVERTISEMENT. 



The present publication is the second part of a work on North 

 American Diptera in process of preparation by Dr. H. Loew, of 

 Meseritz, Prussia, undertaken at the especial recpiest of the 

 Smithsonian Institution. The materials have been derived prin- 

 cipally from the collection of Baron R. Osten Sacken, Consul- 

 General of Russia in New York, kindly intrusted to the author 

 for examination. 



The work will appear in monographs of genera and families, 

 sufficient materials being on hand for illustrating particular groups 

 only, without relation to their systematic sequence. 



The Institution is under obligations to Baron Osten Sacken for 

 superintending the translation of the work from the German manu- 

 script, and editing it, as well as for correcting the proof-sheets. 



JOSEPH HENRY, 



Secretary S. I. 

 Smithsonian Institution, 



Washington, January, 1864. 



PHILADELPHIA: 

 COLLINS, PRINTER. 



