308 ■^- H. Clark. , 



1. The Atlantic Criiioid-Fauna. 



The crinoid faima of the Atlantic Ocean and of tlie adjacent enclosed 

 seas is composed of types all of which are very closely related to the 

 characteristic types of other areas, and none of which can in any way be 

 assumed to have arisen in their present habitat. 



There are plainly indicated four paths of migration by which crinoids 

 have intruded into the Atlantic from other regions, two of which are now 

 closed. These fonr paths of migration are: — - 



1. From the Arctic. The crinoids which have intruded into the Atlan- 

 tic from the Arctic Ocean are all inhabitants of very cold water, and they 

 are more or less sharply differentiated in habitat from the crinoids from 

 other sources by a distinct temperature barrier, being confined exclusively 

 to far noi'thern waters. 



The Arctic crinoid fauna appears itself to be in the main a derivative 

 from the fauna of the Indian Ocean and of the Pacific region generally, as 

 represented in the Bay of Bengal, to which is added an antarctic element. 

 It occurs outside of the Arctic Ocean and north Atlantic Ocean only in the 

 seas of Japan and Okhotsk, where it is characteristic of the belt of very 

 cold water along the Asiatic shores from Korea northward. The antarctic 

 element in this portion of the arctic realm is not the same as that in the 

 arctic ocean. 



2. From the southern Indian Ocean. The deep water crinoids of the 

 Atlantic are all representatives of types characteristic of the deep water 

 of the Indian and Pacific Oceans and of the waters about southern Africa 

 and further southward ; these types do not occur in the Magellanic region. 



This route should probably be considered as in reality only a part 

 of the succeeding, including the deeper water species characteristic of it ; 

 but as it is still open to migration while the succeeding has long been 

 closed it seems best to keep them separate. 



These deep water crinoids, like those of the shallow water, are better 

 represented on the western than on the eastern side of the Atlantic. 



In the Pacific Ocean we find a curious state of affairs: the Antarctic 

 fauna, as represented by its Magellanic subdivision, extends uninterruptedly 

 northward from the Magellanic region along the coast of South and North 

 America to Alaska, passes westward along the Aleutian Islands to Kamt- 

 chatka, and thence southward along the Kuril Islands and the Pacific coast 

 of Japan as far as Tokyo Bay where it occurs in the samo localities and 

 depths as certain Clements of the East Indian fauna. 



