PILSBRY : NON-MARINE MOLLUSCA OF PATAGONIA. 



619 



did not gain access to the eastern Brazilian plateau. If the conclusion that 

 the Amazon valley was a Cretaceous bay or strait connecting the Atlantic 

 and Pacific be well-founded, then the common dispersion center of this 

 old fauna may have been in land now lost under the Atlantic. The facts 



FIG. 25. 



Distribution of Tomigerus, Anostoma and Auris, three old genera common to the Brazilian and 

 Guiana-Colombian centers (probably all are more widely distributed inland). 



FIG. 26. 



FIG. 27. 



so 



Distribution of Odonlostomus. 



Distribution of (i) Macrodontes, (2) Anctus, 

 (3) Hyperaulax and Bonnanius. 



of molluscan distribution favor the view that in Archhelenic times the 

 Amazon valley formed a gulf opening westward, wherein Cretaceous deposits 

 were laid down ; eastern Brazil north to Guiana bounding this gulf on the 

 east, until the depression of the Atlantic basin marked the close of Mesozoic 



