1897] DISTRIBUTION OF PELAGIC FOBAMINIFERA 21 



regions Globigcrina dutcrtrci and pachy derma, together with very 

 minute specimens of Globigcrina bulloidcs, appear to be the only forms 

 present in the surface waters. The gradual disappearance of the 

 tropical species, and their replacement by other species, as the colder 

 water to the north and south of the equatorial regions is entered, has 



Fig. 2. — Orbulina imiversa (d'Orbigny), from the surface. 



always appeared to me rather puzzling, especially when it is re- 

 membered that these changes take place in a continuous oceanic 

 current, like the Gulf Stream, flowing from the equator towards the 

 poles. It sometimes seemed as if the one form slowly passed into 

 the other with the changed conditions of surface temperature. 



The same species inhabit all the great oceans, but in the Indian 

 and Pacific Oceans certain species appear to predominate, for 



