172 BALANID.E. 



Geological History. 



The ancient history of the Balanidae is a brief one. No 

 secondary species has hitherto been discovered ; in my 

 monograph on the fossil Lepadidaa* I have shown that the 

 negative evidence in this case is of considerable value, and 

 consequently that there is much reason to doubt whether 

 any member of the family did exist before the Eocene 

 period. The existence of a Cretaceous Verruca is an appa- 

 rent exception to the rule, as this genus has hitherto 

 always been ranked amongst sessile eirripedes; but Verruca, 

 as we now know, must be placed in a family by itself, 

 quite distinct from the Balanidae. Balanus is the oldest 

 genus as yet known ; it first appeared in Europe and North 

 America, during the deposition of the eocene beds ; and 

 was at that time, as far as our information at present serves, 

 represented by very few species. In South America, one 

 species of Balanns abounds in individuals in the ancient 

 Patagonian tertiary formation. I have seen, in the British 

 Museum, specimens, said to have come form the eocene 

 nummulitic beds near the mouth of the Indus, belonging to 

 the second section of the genus. Generally, the extinct forms 

 belong to the last section of this genus, which has the 

 parietes not permeated by pores. During the miocene 

 and pliocene ages, sessile eirripedes abounded. No extinct 

 genus in this family has hitherto been discovered. It is 

 singular, that though the Chthamalinae approach much 

 more closely than do the Balaninae to the ancient Lepadidae, 

 of which so many species have been found fossil even 

 in the older Secondary formations, yet that only one 

 species of one genus of this sub-family has been hitherto 

 found in any deposit ; and that species is the still existing 

 Pachylasma giganteum, in the modern beds of Sicily. 

 During the epoch of the Glacial deposits in Scandinavia, 

 Scotland, and Canada, the still existing species seem to 

 have abounded ; and they attained larger average dimen- 



* ^ince the note to page 5 of that work was written, 1 have been informed 

 that the so-called cretaceous Tubicinella maxima is not a Cirripede. 



