INTRODUCTION. 
Tae completion of the Volumes dealing with the very rich Rhopalocerous fauna of 
Mexico and Central America has been inordinately delayed from various causes—the 
constant pressure of other work, the ever-increasing amount of material, the gradually 
failing health and subsequent death of my colleague, Osbert Salvin, and the great 
difficulty of dealing with the Hesperiide. Salvin, however, lived long enough to help 
me conclude all but the Pamphiline and the latter part of the Supplement. The difficulty 
with the Hesperiidz was, in a measure, solved, in 1893, by the publication of Watson’s 
classification of that family, and our arrangement of the Pyrrhopygine and Hesperiine 
is mainly based on that author’s system ; the Pamphiline, however, were left unfinished, 
and but little use could be made of his work on these insects. Moreover, on 
commencing our study of the Hesperiide we found it necessary to dissect and examine 
the genitalia of the males of various critical species; and this led us to continue the 
process to the whole of them, a work requiring much time, but amply repaid by the 
_ results, as may be seen by a reference to our Plates. As an instance of the importance 
of these characters, we may note that in Thanaos several of the species are 
absolutely inseparable by external peculiarities, but markedly different in their genital 
structure. 
Our study of the Central-American butterflies proves conclusively (1) that the 
fauna is mainly a northern extension of that of Tropical South America, extending on 
the Pacific side to Mazatlan and on the Atlantic to a little beyond Ciudad Victoria in 
Tamaulipas, some few species on each coast reaching the Southern United States, 
with, of course, many peculiarly modified forms in the region; (2) that there are a 
considerable number of Nearctic genera and species coming down the central plateau 
a certain distance into Mexico and some even into Guatemala, as Argynnis, Vanessa, 
Limenitis, Grapta, various Colias, &c.; (3) that there are no strictly alpine forms, the 
insects met with above the tree-line being mostly stragglers from below, such species 
