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INTRODUCTION. 



The principal object of the present Catalogue has been 

 to give a complete list of the specimens of Dipterous Insects 

 contained in the collection of the British Museum, indicat- 

 ing at the same time the peculiarities of each, as regards 

 variations of character, locality, and the source from whence 

 it has been derived. With this view, the different individuals 

 of each species contained in the collection are indicated by 

 the letters a, b, c, &c, following the name of the species and 

 its synonymes, and the description, if it appeared to have 

 been before undescribed. 



This part of the Catalogue of Dipterous Insects has been 

 prepared and the new species described, by Mr. Francis 

 Walker, so well known for his attention to this order of 

 Insects. 



The remaining parts, containing the other families, are in 

 hand, and will follow as soon as they can be completed. 



JOHN EDWARD GRAY. 



British Museum, 

 March 15, 1849. 



