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. 
