252 ANIMALS OF THE SEA FLOOR 



As regards the geographical distribution of the 

 animals inhabiting moderate depths, it may be said, 

 speaking very generally, that the character of the fauna 

 is determined rather by temperature than by geogra- 

 phical position. Thus it is found that genera and 

 even species of animals, which may be dredged at a 

 depth of a few fathoms in the Arctic regions, occur at 

 greater depths in the more southern parts of their 

 range, where the shallow water is too warm for them. 

 For example, a certain starfish which is found com- 

 monly off the west coast of Ireland between 300 and 

 400 fathoms, and which stretches as far south as the 

 Bay of Biscay in deep water, occurs at a depth of 

 15 fathoms within the Arctic circle. Again, the current 

 of relatively cold water which runs northwards along 

 the west coast of South America allows many of the 

 southern types to extend far to the north, and carries 

 the characteristically subantarctic Isopod genus Serolis 

 to the coasts of Southern California. 



It is possible to divide up the shallow water of the 

 globe into regions whose faunae differ from each other, 

 both in the actual species which compose them, and 

 also in the general proportion in which the various 

 groups of the animal kingdom are represented. Thus 

 it is found that the fauna of the shores of East Africa 

 has a much closer resemblance to that of India and of 

 the Pacific than it has to that of South or of West 

 Africa. Similarly, the fauna of the north-east coast 

 of the United States has more species in common with 

 that of the western shores of Europe than with that 

 of the West Indies. In a recent work (Ortmann, 

 " Grundziige der Marinen Tiergeographie ") the coastal 

 waters of the globe, down to 100 fathoms, have been 

 divided into a number of faunistic regions which may 

 be briefly mentioned here. 



