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 tire 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, 
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. 
