276 



DISTINCTIVENESS OF 



by an asterisk occur fossil in the Mediterranean 

 area, and form a large proportion [59 to 70] of such 

 as have had a lengthened settlement in the Medi- 

 terranean area. 



When treating of marine zones or provinces we 

 are too apt to consider them as denned by hard 

 lines, whereas no certain limits can ever be drawn. 

 The northern Atlantic has certain common specific 

 forms, with a great range from north to south ; and, 

 in addition, there are the characteristic forms of 

 the province. With respect to these, the difference 

 presented by each successive breadth of sea consists 

 in the numerical decrease of the individuals of a spe- 

 cies from the place where it is typical. As we move 

 south we part with northern forms, and vice versa. 

 This process holds good, not only with the shelled 

 Mollusks, but with every other class. The Octopus 

 vulgaris has a great range, and is a common form 

 through several provinces — the Boreal, the Celtic, 

 the Lusitanian, and along the whole of the African 

 coast as far as the Cape. But, as a whole, the Ce- 

 phalopods can be readily referred to zoological 

 zones. This Octopus, however, is common along 

 the eastern coasts of Africa, including the Bed. Sea ; 

 and it occurs there, not because at some past time 

 it passed from the Mediterranean, but because this 

 particular form is equally a constituent of the East- 

 ern as of the West African fauna. 



The abundance of stony corals is one of the cha- 

 racteristics of the Bed Sea. Some few are common 



