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. Kobelt 

 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 

 same 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 J 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, 0., " Verwandschaftsbeziehungen d. Helix Arten," p. 116. 

 t Andreae, A., " Binnenconchylienfauna d. Miocans," II., p. 31. 

 \ Woodward, S. P., " Manual of the Mollusca," p. 112. 



