INTRODUCTION. 7 



As affording some standard of comparison by which to compare the number of species 

 found fossil in any Tertiary deposit, in relation to the number of species probably existing 

 in the neighbouring seas during the same epoch, I may state that there are now living and 

 propagating on the shores of Great Britain, eleven species belonging to the two Families 

 included in the above table. In the Coralline crag, which seems to have been emi- 

 nently favorable for the existence and subsequent preservation of Cirripedes, and which 

 has been so well worked, nine fossil species of these two families, as may be seen in the 

 table, have been discovered. 



