PREFACE. 



IT was originally contemplated to give a complete enumeration, 

 with descriptions, of the British DIPTERA in three volumes, of 

 which the present is the last, and a general Introduction was pro- 

 mised therewith. But, as has been already explained in the 

 Preface to the second volume, the matter was found so much 

 more extensive than had been calculated, that it became neces- 

 sary to omit a large proportion of the recorded British species, 

 and many of the genera in the vast Family Mnscida. It would 

 require a fourth volume to develope the work with the degree of 

 completeness originally proposed ; and as there is now a prospect 

 that the Publisher may be encouraged to offer such a supple- 

 mentary volume by Mr. Haliday, it has been thought better to 

 reserve the general view and illustrations of the Order for the 

 conclusion, and thereby to give more space for the treatment of 

 the Families remaining for the present volume, and for additions 

 to the plates, and to the text, illustrative of those treated of in the 

 preceding two. A complete enumeration of the known British 

 species not described in these three volumes would have occupied 

 more space than could be spared for the purpose. The additions 

 therefore have been limited to a notice of the genera omitted, 

 including the reasons for the exclusion of some few that appear 



