INTRODUCTION. 



The first portion of this Volume of Diptera, pp. 1-216, dealing with the Families 

 Cecidomyiidae — Empidae, was contributed by Baron C. E. Osten Sacken, and published 

 in 1886-87. The Supplement, pp. 217-376, is based mainly on the collections made 

 for us in Mexico, in 1888-89, by Mr. and Mrs. Herbert H. Smith. This large amount 

 of additional material has been worked out by well-known American Dipterists, the 

 Families Mycetophilidae — Asilidae (there were no additional specimens of Cecidomyiidae, 

 Blepharoceridae, Chiromyzidae, or Xylophagidae) by Professor S. W. Williston, the 

 Dolichopodidae (of which we had scarcely any representatives previously) by Professor 

 J. M. Aldrich, and the Empidae by Professor W. M. Wheeler and Mr. A. L. Melander. 

 On pages 377-378 a list of the species recorded from Mexico or Central America 

 since 1887, and not identified or mentioned in the Supplement, is given, some of 

 which may possibly prove to have been here described by Prof. Williston under other 

 names. Amongst these insects is a species of Psychodidae, not a single representative 

 of this family having been received by us. The six coloured Plates have all been 

 prepared by Mr. Wilson of Cambridge, from drawings made by the late F. M. van 

 der Wulp, or (the Dolichopodidae) by Mr. J. E. Collin of Newmarket. The index to 

 the three Volumes of this subject will be inserted at the end of the last one, when 

 completed. 



Ed. 



December 1901. 



