On the Geographical Distribution of Insects. 175 



American by its geographical situation, would in reality be 

 European by its entomology. Canada and the north of the 

 United States possess, in like manner, a multitude of our 

 species. We there find Brachinus crepitans, Dermestes muri- 

 nus and vulpinus, Vanessa antropa, V. album, cardui and ata- 

 lanta, Polyommatus argiolus, Hesperia comma, Zygcena ono- 

 brychis, Vespa vulgaris, Ophionluteus, Fentatomajuniperina, 

 Cercopis spumaria, Helophilus pendulus, &c, &c. Mexico has 

 a much smaller number, for hitherto there have only been 

 found Vanessa atalanta and Cardui, at Vera Cruz, and Der- 

 mestes vulpinus, in California. Finally, we are unacquainted 

 with any other of our insects in the whole of South America 

 than Vanessa cardui, Corynetes and Pristonychus, of which 

 we have already spoken. 



In general, it is not the richest genera which furnish the 

 most sporadical species, as the above examples prove, since 

 they are taken for the most part from genera not very nume- 

 rous in species. We have only further to examine the great 

 genera Cicindela, Carabus, Bister, and Chrysomela, to lie con- 

 vinced of the truth of this assertion ; but it cannot be made 

 without the admission that there are pretty frequent excep- 

 tions, particularly among the Lepidoptera. 



It might be supposed also, that the sporadi-ity of species is 

 in direct relation with that of genera ; that is to say, that the 

 most sporadical species are found in the most sporadical o-e- 

 nera ; but the exceptions in regard to this are so numerous, 

 that it is not easy to say on which side the rule lies. The 

 sporadicity of the two groups in question rests, in truth, on 

 diifereut foundations. That of genera appears to be in rela- 

 tion with the number of their species, while that of species 

 lias no connection with the number of their individuals ; and it 

 is very easy to conceive an eminently sporadical genu.s, which 

 may be composed of species peculiarly endemical, but nume- 

 roas and every where diffused. This case, however, does not 

 seem to be exemplified in nature. 



It is scarcely necessary to direct attention to the fact, that 

 the inverse takes place in the reciprocal endemicity of genera 

 and species, and that we cannot conceive an endemical genus 



