624 PATAGONIAN EXPEDITIONS: ZOOLOGY. 



In molluscan distribution, there is strong evidence against the view 

 of Ortmann (1902, p. 347) that the northern margin of South America 

 formed part of the Antillean continent. Schuchert's representation of the 

 Caribbean Sea as an old permanent basin seems preferable ; but his repre- 

 sentation of the total submergence of the Antilles in the Middle Cretaceous 



FIG. 31. 



Distribution of Helicida of the group Belogona Euadenia (one species extends westward to 

 eastern Europe). 



and again in the Upper Oligocene 1 cannot, I think, be sustained. The 

 rich Oligocene beds of Jamaica (Bowden) and Santo Domingo, carrying 

 a marine fauna of littoral type, occur at very low levels ; and no deposits 

 actually known to be Oligocene are found on the higher mountains, which 

 I believe were islands in both Cretaceous and Oligocene times. 



The primary region of radiation of the middle American families named 

 above is a subject too large for adequate discussion in this place. So 

 much is clear : the fauna contains three groups of diverse genesis. The 



'Bull. Geol. Soc. Amer., XX,'_P1. 95, 97, 1910. 



