10 IOWA STUDIES IN NATURAL HISTORY 



fusion of the structure with the club. The first has apparently 

 taken place in the Pamphilinae and the second in the Hesper- 

 iinae. The relation of the length of the apiculus to the thickness 

 of the club has been used extensively to separate certain genera 

 of the Pamphilinae but I find that its value is limited. It is 

 variable in most species, and only where extremely short or ex- 

 tremely long is this variation negligible. In such species as 

 verna the apiculus is sometimes longer and sometimes shorter 

 than the thickness of the club and is always difficult to measure 

 with satisfactory accuracy. The length of the entire antennae 

 measured in proportion to some other part of the insect is useful 

 to distinguish a few genera of our fauna. 



The legs offer three important characters, viz., the presence or 

 absence of the epiphysis on the front tibiae, the presence or ab- 

 sence of spines on the mid tibiae and to a certain extent their 

 form, and the number of pairs of spurs on the hind tibiae. The 

 epiphysis does not concern us in a study of the North American 

 fauna and the spurs on the hind tibiae characterize only one 

 genus, but the spinulation of the mid tibiae is useful in several 

 cases and in spite of some evidence to the contrary, I believe that 

 it is a good character, at least to the extent used in this paper. 



The wings vary greatly in shape, sometimes in a striking way, 

 as in Eantis, Systasea and Goniunis. In certain others, as Atry- 

 tonopsis, they have a distinctive form which is less useful because 

 less pronounced in the female and difficult to characterize. The 

 neuration is of comparatively little use beyond a few conspicuous 

 features, for it is impossible to pick a reasonably long series of 

 related species without finding some transition in all of the 

 salient features. In spite of this I have made use of the position 

 of vein 11 of the primaries to separate Chiomara from Thanaos, 

 but in this case there seem to be other grounds, and the one vein 

 furnishes a convenient and apparently reliable corollary. The 

 distance between the bases of veins 6 and 7 of the primaries of 

 Pholisora is greater than in most other genera. The relation of 

 vein 5 to 4 and 6 in the primaries distinguishes the Megathy- 

 midae and most Pamphilinae from the other skippers, and helps 

 to separate some genera. The position of veins 2 and 3 of the 

 primaries is another character which must be used with caution, 

 for these veins vary in closely related species and can be depend- 



