264 



SPECIES WITH WESTERN RELATIONS. 



common to both sides of the Atlantic, will repre- 

 sent the remaining portion of the fauna of that 

 earlier stage of the Atlantic when it was closed at 

 its northern extremity, so far as that fauna has been 

 able to live on. 



With a change so great as that here indicated, 

 a large proportion of the original marine fauna 

 of the Boreal province of either side of the At- 

 lantic must have been totally extinguished, whilst 

 of the forms that continued to live on, there are 

 some that exhibit characters which deserve notice. 



Pholas crispata is one of the shells of those 

 Selsey beds of early date, w^hich have already been 

 referred to : as it occurs there, it is remarkable on 

 account of its abundance, and great size, being more 

 than as large again as any living specimens to be 

 now met with in European seas. This shell, with 

 like dimensions, is found fossil in Ireland, in some 

 old sea-beds : as a species, it had its maximum 

 at an early stage of the Atlantic fauna, and it 

 has lived on. Ed. Forbes describes its present 

 distribution, as a British species, to be Atlantic, 

 ranging north into our Boreal province. It is 

 one of the forms common to both sides of the At- 

 lantic, and on the American coasts it occurs as far 

 south as Carolina. This species therefore, though 

 sufficiently common now in our European seas, 

 may be considered to have had western relations 

 originally, to have found more suitable conditions 

 for its development in the earlier Atlantic, and 



