INTRODUCTION 



The family Megathymidae, or "giant skippers" is limited to a 

 very small number of species, but owing to the comparative rarity of 

 most of these forms no detailed study of the family as a whole has 

 ever been attempted. Owing to the painstaking work of Riley our 

 knowledge of a single species {yuccae) is far in advance of that of 

 any or all of the others, and we are not only familiar with its struc- 

 tural details, but also possess considerable information concerning its 

 very interesting and peculiar larval stages. 



In the present work we have attempted to gather together any 

 stray biological facts which have from time to time been published 

 and also to present a comparative study of the various members of 

 the group based on structural features. In some instances, owing to 

 lack of material for dissection, our work is naturally very incomplete, 

 but in several of the more obscure species we have been fortunate 

 enough to have had a large number of duplicates at our disposal, 

 which has not only been of great value for structural studies, but has 

 also aided us materially in determining the range of variation of the 

 general wing-pattern. 



In the course of our investigations it soon became clear to us that 

 considerable confusion exists not only with regard to the species 

 thmselves, but also concerning the two sexes of several species ; 

 erroneous identifications exist, females have been falsely described as 

 males, secondary sexual characters have been considered as specific, 

 and wrong figures have added to the general confusion; we have 

 therefore considered it advisable to present half-tone figures of both 

 sexes in those instances where no accurate figures exist and our ma- 

 terial was such as to permit of being photographed. We have placed 

 a * before those references which contain a figure. 



Owing to the size and strongly chitinous nature of the $ genitalia 

 we have abstained from mounting them on slides "in toto," finding that 

 much better results could be obtained by dissection and separate mount- 

 ing of the various portions ; by this method a distortion of the parts 

 was avoided and more accurate drawings of the minute details made 

 possible. 



