438 Transactions. — Miscellaneous. 



North America. They therefore cannot have immigrated hy 

 way of North America, but dm^ing different geographical con- 

 ditions. 



Between the Ohgocene and the end of the Pliocene period 

 South America was completely isolated, and therefrom it 

 derives its peculiarity in flora and fauna. It was only at the 

 end of the Pliocene, or perhaps even later, that North Ame- 

 rican mammals appeared in South America, whilst in return 

 South American ones advanced to Mexico. There are no dif- 

 ferences of opinion on this point, and the geology of Central 

 America tells us that the Isthmus of Panama did not come 

 into existence before the end of the Tertiary era. But it seems 

 that many scientists think that a land-connnunication be- 

 tween North and South America might have existed in the 

 beginning of the Tertiary era. No doubt many circumstances 

 have here to be taken into consideration, as, for example, the 

 communication of Florida with the West Indies, as proved by 

 the Miocene land-shells of Florida, elaborately described by 

 Dall, and the many changes which have taken place within 

 the area of the West Indian Islands, a reliable judgment on 

 which we are unable to give at present ; but, as for the older 

 period, we must, in my opinion, admit a sharp separation 

 between the territories of North and South America. The 

 fresh-water fauna of both shows enormous differences, in the 

 Naiadae and other molluscs, as well as in the fishes, tortoises, 

 amphibians, &c. North America, with its Cyprinidce, Uro- 

 dcla, &c., is m all these points more nearly related to the 

 palsearctic region, while South America — that is to say, Archi- 

 guyana — shows close alliances only to Africa. W^ith regard to 

 the fresh-water fishes this is so well known that I need not 

 dwell on it further, but I would point out that the old com- 

 mon features have been obscured through later relations to 

 the Mediterranean and Indian faunas, wherefrom many ele- 

 ments have been absorbed. 



After the upheaval of the Isthmus of Panama, mammals, 

 birds, and Lepidoptera of the adjoining countries rapidly be- 

 came mixed, and this was also the case with all the other 

 rapidly-wandering creatures. Thus we see Cinosternwn and 

 other tortoises immigrate to the north of South America; even 

 two species of Urodcla {Si^clcrpcs) advance as far as Ecuador ; 

 and even more noticeable is the exchange of Batrachia and 

 LacertidcB. Nobody will deny the importance of studying 

 separately the two elements of South America if an account 

 is to be given of the geographical distribution of the frogs. 

 Ilanidcs are missing in Archiplata just as completely as 

 Aglossa, Urodela, and others, but are found in Ecuador and 

 Columbia. The Aglossa and Dendrohatidce are restricted to 

 Archiguyana, Africa, and Madagascar. Even some genera of 



