278 OKIGIN OF LIFE IN AMERICA 



problem. This problem has been approached from many 

 other points of view. On the evidence of the fossil marine 

 mollusks of the West Indian and the Mediterranean regions, 

 Mr. Guppy* concluded that a migration must have taken place 

 right across the Atlantic along an ancient shore-line. More 

 recently, Professor Gregoryf dwelt upon the intimate affini- 

 ties that exist between the fossil sea-urchins of the West 

 Indian and Mediterranean areas, and urged that it could only 

 be explained by the assumption of a belt of shallow water 

 across the Central Atlantic in, at latest, Miocene times. A 

 few years later he adduced evidence from the fossil corals of 

 Barbados, that the West Indian fauna is only a fragment 

 of that of the Mediterranean Miocene, having received 

 nothing from the Pacific. That this fauna did not follow 

 along the shores of the North Atlantic basin is shown 

 by its absence from the northern Miocene of Europe and 

 America. J Mr. Guppy has lately renewed the discussion of 

 this subject and once more affirmed his adherence to the 

 theory he expressed long ago, which has meanwhile received 

 so much additional support. Even the recent marine fauna of 

 the Antilles is intimately related to that of the Mediterranean. 

 Some of the faunistic marine affinities between the two re- 

 gions referred to might just as well have been produced by a 

 dispersal along a land bridge between Africa and South 

 America. Such, for instance, is the occurrence in early Ter- 

 tiary deposits of the aquatic snake Pterosphenus in Egypt 

 and Alabama. Dr. Andrews, || indeed, thought it yielded an 

 argument in favour of the more southern land connection. 



Let us now examine what light the recent marine mammals 

 inhabiting the Caribbean Sea and the Gulf of Mexico throw on 

 the problem. On the south-east coast of Florida we meet with 

 one of the most curious of American mammals. With 

 its seal-like head and flattened tail it is at once recognised as 

 something quite distinct from other marine creatures. The 



* Guppy, E. J. L., " West Indian Geology," p. 501. 

 t Gregory, J. W., " American and European Echinoid faunas," 

 pp. 101108. 



t Gregory, J. W., " Geology of the West Indies," p. 307. 



Guppy, E. J. L., " Geological Connexions of the Caribbean Eegion." 



l| Andrews, C. W., " Tertiary Vertebrates of the Fayum," p. xxv. 



