INTRODUCTION. XX1X 
Additions may yet be expected from the Atlantic slope of Chiriqui, in the State of 
Panama, and from the Isthmus of Darien, districts almost unworked; and, to judge 
from a small collection made by Mr. Becker in the neighbourhood of Durango city, 
other northern forms are likely to occur in that part of Mexico. 
Two important collections of Rhopalocera acquired long ago by us have been of 
great assistance in working out the Central-American species, viz., that of H. W. 
Bates, including the first set of his captures on the Amazons (in all 11,450 specimens), 
and that of Herbert Druce, containing the types of many Costa Rican insects described 
by Dr. Butler and himself. The late Dr. Staudinger, to whom our thanks are due, 
communicated numerous types of Mabille and Herrich-Schaffer, so that we have been 
able to determine with certainty many of the species described by these authors; we 
are also indebted to M. Charles Oberthiir, of Rennes, for assistance in the identification 
of various insects described by Boisduval. On the other hand, all our attempts to 
obtain the loan of Plétz’s quoted (but unpublished) figures of Hesperiide were 
unsuccessful, and we have been compelled to leave many of his species unidentified, 
the descriptions being in most cases inadequate for the purpose. I must also here 
record my special thanks to Mr. Champion for the valuable assistance he has rendered 
me, especially in the completion of the Hesperiide, since Salvin’s death. 
Following our usual custom, we have given a distinctive specific name, in preference 
to a varietal one, to such forms (more especially in the genus Papilio) as seemed to be 
confined to a particular district, even if the differences were not very important. 
Since we attach but very little value to relative size, no measurements have, as a rule, 
been given; our numerous figures, however, which are all drawn natural size when 
the entire insect is shown, will supply this deficiency. Where no sex is mentioned in 
the diagnosis, it must be understood that the characters are in almost every case taken 
from the male. 
Of the 113 hand-coloured Plates (including XXIV.a), thirty-four were drawn by 
Mr. R. F. H. Rippon, the remainder by Mr. W. Parkiss, illustrating altogether 
about 1250 species. The dissections of the genitalia and other preparations were 
made either by Mr. A. Cant or by Salvin himself. 
In conclusion, it is a matter of regret that Dr. Holland’s excellent work on North- 
American butterflies, the second edition of which was published in 1900, reached us 
