30 EEPOET OF THE SECRETARY. 



first contemporary authorities in this branch, and principally from 

 materials furnished by or through the medium of the Institution. It 

 contains the description of 716 North American and a list of 507 

 South American species. The plan of this publication is essentially 

 different from that of the synopsis of Lepidoptera, the latter being a 

 mere compilation of existing descriptions, whereas the greater part 

 of the descriptions contained in the former were drawn by Dr. Hagen 

 from specimens in his possession, and thus the necessary uniformity 

 and accuracy have been secured. The original manuscript in Latin 

 was translated into English and prepared for publication by Mr. Ph.' 

 R. Uhler, of Baltimore. 



4. The order of Diptera, (flies, mosquitoes, <fec.,) is known to be 

 exceedingly numerous and of rather difficult study, as much on account 

 of the minuteness and great fragility of most of the species a,s of 

 a peculiar inconstancy and comparative slightness of the characters 

 used for classification. In this case, as in preceding ones, the first work 

 directed by the Institution was one of condensation, namely, the Cata- 

 logue of the described Diptera of North America, by Baron Osten 

 Sacken. It was published in 1858, and includes a list of about 1,700 

 species, with references to ninety -five works and papers containing 

 their descriptions, principally in foreign languages. 



The next thing to be done was either to furnish a republication 

 of all these descriptions, like that of the synopsis of Lepidopterjj, 

 or to attempt at once to prepare a monograph of the order. Owing 

 to the large collections formed by Baron Osten Sacken during his res- 

 idence in this country, the latter Avas possible. It was deemed ad- 

 visable to put these collections into the hands of Dr. H. Loew, of 

 Meseritz, Prussia, one of the most eminent dipterologists now living, 

 who will prepare a series of monographs on the different families of 

 this large order, to be published by the Smithsonian Institution. 

 The first volunie of this series is now in the press. 



It may be proper here to call attention to the great importance of 

 having the first foundation of a study laid by the most eminent 

 authority. This is especially necessary in regard to the Diptera, 

 since, as we are informed, this class of American insects contains a 

 great number of species, closely allied to European species, and con- 

 sequently requires an intimate knowledge of the latter to identify the 

 former. Besides this, there are many insects of the same class in 

 this country altogether different from those of Europe, which Avill 

 require the formation of new genera, a work which can only be prop- 



