IV PREFACE. 



Ortalides, Oscinides and PsiUdes are unnoticed ; but the Sepsides 

 omitted are for the most part mere varieties. The Borhorides 

 and the Hydromyzides are more complete^ and are copied from 

 Mr. Hahday's excellent descriptions of the genera and species of 

 those tribes. The Geomyzides and the Ph'ytomyzides are mostly 

 passed over ; but the (Estrida, the liypocera, and the Bp-ohoscidea 

 are rather fully detailed. Mr. Westwood has again prepared ten 

 plates for this volume, Mr. Haliday's state of health having 

 prevented his contributing the illustrations of the wing-veins of 

 Diptera. 



Prancis Walker. 



Decemher, 1853. 



