36 OUR COMMON BRITISH FOSSILS. 



that the Oldhamia showed, at the articulations of the 

 stems, the positions of the minute cells of zoophytes. 

 The most likely idea is that this very pretty and 

 interesting fossil the oldest British organic form with 

 which we are certainly acquainted was related to the 

 little "sea-firs" so abundant nowadays along our 

 coasts. Indeed, not a few of these Sertularians (as 



Fig. 28. a, Sertularia fusca / b, Pinna, with calycles (magnified); c, Plumularia. 

 frutescens ; d, Pinna, with calycles, nematophores, and capsule (magnified). 



they are called) resemble in external shape the 

 hamia. The dry portion that remains when the 

 zoophytes are dead, is of a horny nature, and formed 

 of chitine. This is one of the most indestructible of 

 animal substances, and is likely to be preserved when 

 others would be decomposed. If the Oldhamia had 

 been calcareous, the limy matter would have been 

 dissolved away, and few or no traces of them would 



