PILSBRY: NON-MARINE MOLLUSCA OF PATAGONIA. 



617 



massifs. This connection of the Brazilian and Guiana-Colombian areas 

 must have persisted long after the Archhelenic period, for distinctively 



FIG. 21. 



Distribution of the land-snail family Streptaxidce. 

 FIG. 22. 



Distribution of fresh-water snails of the family Ampnllariidtz, having the operculum wholly corneous. 



American genera had been differentiated. It was interrupted prior to the 

 union with the Antillean-Mexican continent, since the genera of that area 



