272 
ORIGIN OF LIFE IN AMERICA 
existing American forms. The operculate genera Tudorella 
and Leonia of the Mediterranean region are certainly related 
to West Indian forms, though not so closely as was formerly, 
believed. These and other considerations induced Dr. Ivobelt 
to postulate a land connection between Europe and North 
America, which was only severed in Miocene times. The 
German Miocene genus Subulina, the large Glandinae and the 
early Tertiary European Oleacinae, are considered by Pro¬ 
fessor Boettger * as the nearest relations or direct ancestors 
of Central America or West Indian genera and species. The 
samo authority also alludes to the American facies of the 
Tertiary flora of Europe, and concludes that a land bridge 
right across the Atlantic Ocean existed up to early Miocene 
times. Finally Professor Andreaef supports the same theory, 
on account of the occurrence of the West Indian Boltenia, 
Strobilus and Pleurodonte in the Miocene deposits of Silesia 
in Germany. And he was the first to definitely fix the posi¬ 
tion of the land connection as one uniting western Europe 
with the Antillean area. 
Still other features of relationship between these regions 
remain to be considered. Long ago Mr. Woodward $ pointed 
out that the presence of the European genus Clausilia in the 
West Indies and in northern South America (see Fig. 19) 
implied the existence of a former more direct land way across 
the Atlantic than would be afforded by the land connection 
which was supposed to have once united the boreal regions 
of Europe and North America. Since that time others have 
repeated his assertion. Clausilia is now known to have lived 
in Europe since Cretaceous times, and has probably originated 
there. It is partial to high altitudes, large numbers of species 
being found in the Alps, the Dalmatian mountains and the 
Caucasus. Only a single European species resembles the 
American group (Nenia), namely Clausilia pauli of the 
western Pyrenees, and it is so closely related to the members 
of that group that both Mr. Bourguignat and Mr. Locard, 
two French conchologists of the “ nouvelle ecole,” failed to 
find any satisfactory difference between them. It is quite 
* Boettger, O., “ Verwandschaftsbeziehungen d. Helix Arten,” p. 116. 
f Andreae, A., “ Binnenconchylienfauna d. Miocans,” II., p. 31. 
f Woodward, S. P., “Manual of the Mollusca,” p. 112. 
