PREFACE. 



THE following descriptions are prepared from British or Irish 

 specimens ; and the species which are doubtful natives of Great 

 Britain and Ireland, or which I have not had the means of 

 examining, are omitted. The Diptera are here divided into 

 Suctoridea, Proboscidea, and Eproboscidea : the Proboscidea com- 

 prise the Nemocera, Brachycera, and Hypocera ; and this volume 

 contains the families of Brachycera in which the Diptera are 

 most highly organized, or have their characters most developed. 

 Mr. Haliday has contributed the characters and synoptical tables 

 of the Diptera, of the Empidte, and of the Syrphida, and the 

 whole of the Doliekopida ; and I am also indebted to him for 

 his kind assistance in other parts of the volume. The ten plates 

 are prepared by Mr. Westwood ; two others, by Mr. Haliday, 

 illustrating the wings of Diptera generally, will appear in the 

 next volume. 



The last volume will contain an introduction and general 

 observations on these insects. 



FRANCIS WALKER. 



December, 1851. 



