GEOLOGICAL HISTORY. 173 



sions than the same species now do on the shores of Great 

 Britain, or even on the shores of the northern United States, 

 where the average size seems larger than on this side of the 

 Atlantic. 



Under the genus Balanus, I have given my reasons for 

 never naming species in this large and difficult genus, with- 

 out examining the opercular valves : it has been owing to 

 this, as it appears to me, proper want of caution, that there 

 are so many nominal species. Thus it is made to appear in 

 catalogues, that the tertiary seas abounded with species 

 of Balanus to an extent now quite unparalleled in any 

 quarter of the world. Bronn,* for instance, in his invaluable 

 1 Index Palseontologicus,' gives the names of 35 Balani, 

 found fossil in Europe, and I have not counted those found 

 only in alluvial deposits, as they would certainly be the same 

 as the still living species. Now I know only 11 recent 

 Balani on the shores of all Europe, from the North Pole to 

 lat. 30° ; and of these I doubt whether B. balanoides and 

 improvisus have been found fossil. In the Red Crag there is 

 one extinct Balanus : in the Coralline Crag, which seems to 

 have been very favorable to the existence of Cirripedes, 

 there are six species of Balani, of which two are absolutely 

 extinct, and one does not occur in any neighbouring sea : 

 in the Eocene formations the species seem to have been 

 rare, and I have seen only one, and that is an extinct form. 

 Taking these several facts into consideration, and bearing 

 in mind that Cirripedes usually range widely, I do not 

 believe, if all the specimens of Balani hitherto found in the 

 several tertiary formations, from the eocene to the glacial 

 deposits, throughout Europe, were collected together, they 

 would amount to 20 species. I have myself seen, in a re- 

 cognisable state, only 12 fossil species, of which five are 

 extinct, or not found in any neighbouring sea : I think it 

 probable that three other recent species, viz. B. tulipiformis, 

 perforatus, and ampJdtrite, may occur in the Mediterranean 

 formations ; and this would make 1 5 species. Therefore 

 in the above estimate of 20 species, five are allowed for 



* To save any other person, interested in fossil Cirripedia, going through 

 the several works quoted by Bronn, I have given some remarks on his list ot' 

 species, in an appendix at the end of the Balanidae. 



