While studying the specializations of the wing in the Papilionides, the general results of which are published in the Proc. Am. Philosophical Society, Jan., 1899, I found that Iphiclides, Ajax, Marcellus, etc., differed so strongly from the type of Turnus as to be generically separable. Ajax is, in fact, allied to species having a greenish or yellowish white ground colour, from South America and the Old World, while Turnus is evidently related to the black North American forms, Troilus, etc., with which it flies. This fact enables me to draw the probable conclusion that Glaucus represents the original colour of the species, which, so to speak, is turning into Turnus, The black ♀ Glaucus is the more conservative whereas the males are already, with very rare exceptions, of the yellow tape of Turnus. It is different with certain cases of so-called “melanism,” now spreading in Europe, as Eubyja var. Doubledayaria and Aglia vars. fere-nigra and melaina. Here the original ground colour is changing to black indifferently in both sexes.