78 FOSSIL BUTTERFLIES. 



BUTTERPLIBS OF THE MAYENCIAN (Middle Miocene). 



Only a single one of these butterflies, Mylothrites Pluto, belongs to an extinct 

 genus. Its nearest living representatives are to be looked for in the genera Mylo- 

 thris and Ilebomoia, the former of which finds its highest development in torrid 

 Africa, while the latter is confined to the Indo-Malajan and Austro-Malayan 

 regions. 



The other two belong to modern genera, Eugonia {E. atava) and Pontia (P. 

 .Freyert). These two genera are very similar in their distribution, spreading, like 

 Thanaos, above referred to, over the north temperate regions of both hemispheres. 

 Eugonia, however, is represented equally in Europe and America, while Pontia is 

 considerably richer in species in the Old "World than in the New; yet when we look 

 into the distribution of the neighboring genera we shall find a result somewhat 

 similar to the case of Thanaos. Taking into consideration, in the one case, the 

 present distribution of the genera Hypanartia, Polygonia, Papilio and Hamadryas,^ 

 and on the other of N'eophasia, Tatocheila and Leptophobia, we shall find that the 

 largest development of these groups of genera has been in the New World rather 

 than in the Old, but in those parts of the New World which lie on the tropical 

 confines of the temperate zone. 



Two of the more recent species of fossil butterflies are therefore at home 

 where they are found, although the present development of the group of genera 

 to which they belong finds its fullest expression in America; while the third 

 species follows most of those from the lower tertiaries in seeking its allies of to- 

 day in the tropics of the old world. 



Undoubtedly the material at our disposal is, as we have already remarked, far 

 too meagre to present any generalities of importance, so long as they are unsup- 

 ported by external proof. This aid we can claim in considering the facts we have 

 presented concerning the present distribution of the genera of butterflies most 

 nearly allied to those once living in the neighborhood of Aix. The careful re- 



• I UM Uwu genera in ibe lense Indicated in my HIatorical Sicetcta of generic names. Proc. Am. Acad. Arts, Sci., X, pp. fll-293. 



