iv PREFACE. 



families treated of in this volume are the most difficult and least 

 understood of any, and are in a most unsatisfactory state with regard 

 to their systematic arrangement and identification. It is hoped that 

 this account may spur younger workers on to establish new and 

 important facts, so that inaccuracies may be corrected which naturally 

 will be found in it, and new discoveries made. 



I have to express my thanks to numerous entomologists for kindly 

 help, and for lending specimens to be figured, especially to Miss 

 Ormerod for the loan of blocks from her " Manual of Injurious 

 Insects." 



FRED. V. THEOBALD. 



Cambridge, 1892. 



