INTRODUCTION. 



The principal object of the present Catalogue has been to 

 give a complete Ust of the specimens of Dipterous Insects 

 contained in the collection of the British Museum, indicating 

 at the same time the pecuUarities 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 syno- 

 nymes, and the description, if it appeared to have been before 

 midescribed. 



The Catalogue of Dipterous Insects has been prepared and 

 the new species described by Mr. Feancis Walkek, F.L.S., 

 so well known for his attention to this order of Insects. 



This part contains a revision of the family Acroceridce and 

 part of the family AsilidcB, with a description of the species 

 added since the former parts were printed. 



JOHN EDWARD GRAY. 



British Museum, 



December, 1854. 



