COMPARED WITH THOSE OF EUROPE. 627 



tries ; in tiic latter only two of tiie eight American and four European 

 genera are common to both countries, and in these two the representation 

 is very unequal, one genus, Thanaos, having six* species in America 

 against two in Europe, and the other, Hesperia, fourteen in Europe and 

 two in America. 



In the Vanessidi there are eight genera, of which four are represented 

 on each continent, the others being equall}^ divided between the two coun- 

 tries. ^Ve have naturally in this instance a closer resemblance than in 

 any other group of butterflies, because its genera are mainly genera of 

 the north temperate zone and include some forms common to the two 

 continents. 



In other groups the differences are very observable. Thus, of the nine 

 American genera of Theclidi, but one is represented in Europe, and even 

 in this group (Thecla) the European species have a peculiar facies dis- 

 tinct from the American. Only one of the seven American genera of 

 Rhodoceridi, and two of the seven American genera of Papilloninae are 

 found across the Atlantic ; and in the Pamphilidi only three or perhaps 

 four of the twenty-three genera found in America occur at all in Europe. 

 Or, if we sum up the whole, we may say that of the one hundred and five 

 American genera of butterflies, only twenty-seven or twenty-eight (or 

 about one-fourth) are represented in Europe; and of the others, there 

 are but seven intimately related to European genera. 



A careful study of all other points of resemblance between the two 

 countries will show that they are almost all confined to groups which are 

 boreal in their aspect ; while, if we had excluded from the comparisons 

 the species inhabiting in either country the high north, and had included 

 those of the extreme south, not only would the number of species in either 

 country have been considerably augmented, but the resemblances would 

 have been greatly diminished, and the diflferences more than proportionally 

 increased. Nor would the diflferences appear at their real \ alue if account 

 were not taken, as here, of the lesser structural features for generic dis- 

 tinction. 



In the table on the next page the relative number of species of the different 

 groups of butterflies in Europe and eastern North America is shown, the 

 European species being taken from the last edition of Staudinger and 

 Wocke's Catalogue, omitting the purely Mediterranean forms, as the spe- 

 cies peculiar to the Gulf States have been omitted from the American, f 



* Even this large number has l)een greatly go some change from later discoveries, but as 



increased latterly. the changes would not essentially disturb 



t This list was first published in 187G, in the the comparisons to which attention is here 



Proceedings of the American association for directed, I have not thought it worth while to 



the advancement of science, and on the revise it. 

 American side should undoubtetlly under- 



