PILSBRY : NON-MARINE MOLLUSCA OF PATAGONIA. 629 



southern South America, drained by numerous short, independent rivers, 

 owing to the difficulty of migration and the relative impermanence of the 

 individual streams. 



The presence of peculiar and strongly individualized land snails of 

 Brazilian type [Scalarinella, Plagiodontes, etc.) in the Sierras of western 

 Argentina and the now isolated Sierra Ventana, shows that long ago the 

 Brazilian fauna extended at least as far south as Bahia Blanca, where a 

 fragment has persisted, isolated since the Pliocene at least.^ 



Taking into consideration the climate, the rarity of large forest areas, 

 the aridity of large tracts, and the short, unconnected rivers, we are not 

 inclined to give much weight to Dr. von Ihering's contention that many 

 Brazilian groups are wanting in " Archiplata." So far as mollusks are 

 concerned, that area has very slight claims to rank as an evolution center. 

 I regard the Chilian and Patagonian fauna as an impoverished and slightly 

 modified extension of the fauna of the old Brazilian continent. The evi- 

 dence for an Archiplatan center may be stronger in the case of Crustacea, 

 Oligochaeta, plants and insects ; but I prefer to leave the discussion of 

 these groups to those having first-hand knowledge of them. 



Connected with the Archiplata hypothesis is that of Antarctica, which 

 may here be examined briefly. 



AUSTRAL ELEMENTS IN THE SOUTH AMERICAN 



FAUNA. 



The Austral or Antarctic relationships of the South American fauna 

 have been somewhat fully discussed in other volumes of this series, and 

 a map illustrating the Antarctic continent and its hypothetical former ex- 

 tensions may be found in volume IV. I have to deal here with the evi- 

 dence afforded by the non-marine mollusks, which, taken by itself, leads to 

 the following conclusions : (i) There is no evidence that Antarctica was 

 ever an evolution or radiation center for non-marine mollusks, though 

 there is some evidence showing that it served as a highway for migration. 



(2) There is some evidence of migration from South America to Austral- 

 asia, but at present no evidence of a counter movement to South America. 



(3) Nothing in the distribution of mollusks would lead to the hypothesis 



' Dr. Ortmann agrees with von Ihering in isolating a Chilian and southern Patagonian land 

 mass of Cretaceous age, but he views it as an e.xtension of Antarctica. The difference is rather 

 one of names than of things. Proc. Amer. Philos. Soc, 1902, pp. 379, 381. 



