280 ORIGIN OF LIFE IN AMERICA 



the Eocene Prorastomus, which must be looked upon as the 

 ancestor of Trichechus. I mentioned before that Proras- 

 tomus has been discovered in the Eocene of Jamaica. The 

 teeth of another form (Prorastomus veronensis) are known; 

 from Italy. Thus the affinity still existing between the South 

 American and West African forms was apparently fore- 

 shadowed already during the Eocene Period by the relation- 

 ship of the two species of Prorastomus, the ancestors of the w 

 modern manantees. Dr. Smith Woodward, however, informs 

 me that the relationship of these species is too uncertain to be 

 used as evidence in favour* of an Eocene land bridge. 



All the seals inhabiting the North Atlantic, both on the 

 European and North American side, belong to the genera 

 Halichoerus or Phoca. As soon as we enter the Antillean 

 region these genera disappear, their place being taken by the 

 genus Monachus. On the opposite shores of Europe it is just 

 the same. As far south as Portugal we still find the common 

 seals, but as we enter the Mediterranean we again meet with 

 the same genus Monachus. The Antillean form (Monachus 

 tropicalis), like the Mediterranean Monachus albiventer, 

 seems to be on the verge of extinction. The former was once 

 common off Florida and near most of the islands. Now it is 

 only noticeable in the neighbourhood of Cuba and some of the 

 islands near Yucatan. We can hardly believe, remarked 

 Messrs. Sclater,* that these creatures could easily traverse 

 the whole Atlantic. The hypothesis of a former barrier of 

 land between Africa and America, which we know to be sup- 

 ported by other facts of distribution, would alone explain the 

 difficulty, according to these authors. They only had the sup- 

 posed land connection between Africa and South America in 

 mind, but what strengthens the evidence in support of another 

 more northerly mid-Atlantic land bridge between the Antilles 

 and the Mediterranean region is the fact that the only locali- 

 ties outside the Mediterranean where Monachus albiventer 

 occurs are on the coasts of Madeira and the Canary islands. 



Among the terrestrial species of vertebrates and inverte- 

 brates of the Antilles, as I observed, the affinity with Europe 

 is less marked perhaps than it is in the south-western States 



* Sclater, "W. L., and P. L. Sclater, "Geographyjof Mammals," p. 217. 



