364 ORTMANX — DISTRIBUTION OF DECAPODS [Aprils, 



explains their general absence south of the Amazonas. The exten- 

 sion of the range of these freshwater crabs into Colombia, Ecuador 

 and Peru was not obstructed during the older Tertiary, since 

 during this time these parts became land and were connected with 

 Venezuela. 



Regarding the extension of the old Brazilian mass (Archiplata) 

 to the south, we know that the old Archaic, Paleozoic and Old- 

 Mesozoic rocks continue in southern Bolivia and northern Argen- 

 tina, into the eastern Cordilleras (Suess, 1885, p. 661) ; in Argen- 

 tina, these rocks prevail in the northern parts : they are also found 

 in the Pampean Sierras,^ but do not seem to extend southward beyond 

 the province of Buenos Ayres (Suess, 1885, p. 664). To the south 

 of these parts the whole of Patagonia was apparently covered by the 

 Cretaceous sea (Suess, 1888, p. 68;^, and above, p. 338J. The 

 Brazilian continent was also surrounded in the west by Jurassic and 

 Cretaceous sea, as is demonstrated by the presence of the respective 

 deposits in the region of the Chilian-Argentinian Cordilleras (see 

 p. 338). As we have seen above {ibid.), it is very probable that 

 during the Jurassic and a larger part of the Cretaceous era, the 

 Brazilian mass was separated by this sea, which occupied present 

 Patagonia and the site of the Cordilleras, from another continental 

 mass lying to the west, southwest and south of it, which was formed 

 by the present Chilian coast range and its southern continuation, 

 which belonged, at least during the Cretaceous, to the Antarctic 

 continent. At the end of the Cretaceous a land period began in 

 these regions which culminated in the Eocene, and which effected a 

 connection of the old Antarctica with Archiplata, chiefly in the 

 region of the Chilian-Argentinian Cordifleras. This connection 

 made possible the immigration of Parastacus into the southern parts 

 of Archiplata (Argentina, Uruguay, southern Brazil), and it has 

 remained up to the present time, although parts of Patagonia were 

 again submerged during the course of the Tertiary. 



The results obtained in the foregoing concerning the history of 

 the American continent may be summed up as follows. 



I. America originally consists of three parts : North America (its 

 nucleus being in the East), the Antillean continent (comprising the 

 West Indies, Central America and the northern coast of Venezuela) 

 and the old Brazilian fnass (Archiplata). Also a fourth part enters 



* Valentin, J., Bosqiiejo geologico de la Argentina, 1898. 



