THE EUROPEAN SEAS. 



227 



of 29° would have to sink upwards of 100 feet 

 for every degree it migrated south. In like man- 

 ner, should a change in the temperature of any 

 marine province be brought about (and this has 

 happened repeatedly over the European area), as, 

 for instance, from cold to warm, the marginal forms 

 could only continue their existence by moving to 

 greater depths. The case is here put in a purely 

 hypothetical form, for no marine animals are so 

 exacting in their requirements ; very many forms 

 have a range in depth in the same latitude, which 

 is considerable, and many have a broad horizontal 

 range. Such being the real condition of the ques- 

 tion, a general, and not a close relation of distri- 

 bution in depth to distribution in latitude is all 

 that can be expected. 



Mr. M 'Andrew has made an interesting observa- 

 tion, illustrative of the distribution of species, from 

 temperature dependent on depth. At Mogadore, 

 on the west coast of Africa, in lat. 31° 30', he ob- 

 tained 110 species of Testacea : of these about one 

 half range north as far as to our British coasts ; 

 when, however, the 110 species were divided into 

 two sets, according to depth, eighty-eight ranged 

 from the coast-line down to depths of upwards of 

 thirty fathoms ; amongst these are all those species 

 which are characteristically African or Lnsitanian. 

 Of twenty-two species dredged in thirty-five to fifty 

 fathoms water, all but six were well-known British 

 shells. 



