290 THE FOEAMINIFERA 



dent upon several factors in their conditions of 

 existence, such as the surface and bottom temperatures 

 of the water ; the presence of warmer or colder 

 currents, as, for example, in the Faroe Channel, 

 which, being on the border line between the warm and 

 cold areas, presents a special feature in its foramini- 

 feral fauna ; the'proximity of limestone cliffs ; and the 

 nature of the surrounding sea bottom. As it has 

 already been remarked, a certain proportion of species 

 are cosmopolitan in their habits, being found alike in 

 shallow and deep water ; and in both high and low 

 latitudes. On this statement, however, there must be 

 placed a certain amount of reservation, for there is 

 generally some varietal difference even in these ubi- 

 quitous forms when they are found existing under 

 extreme conditions. 



