INTRODUCTION. vii 



in which the multiplication of their constituent parts is effected is often a subject of great 

 interest for classifiers as well as for physiologists. 



The natural affinities of recent Corals can, in general, be easily recognised by means of 

 facts obtained from these different sources ; but the study of fossil Polypidoms presents 

 greater difficulties, and the palaeontologist must also direct his attention to the modifica- 

 tions which may have taken place after the death of the Zoophyte, and have been 

 produced by the sIgw, but long-continued action of solvent or lapidescent fluids. 

 Changes of this kind sometimes efface the most important features of these organic 

 remains, for it often hai'pens that the different parts of a corallum are not modified with 

 an equal degree of facility, and the complete destruction of certain organs in specimens, 

 where other parts are well preserved, may give rise to most delusive appearances. Even 

 generic divisions have thus been established by some palaeontologists, on accidental changes 

 due to fossilization alone, and it is indeed often very difficult to avoid errors of this kind in 

 the distinction of species, when the observer is not able to compare a sufficient number 

 of specimens. 



§ III. 



This Monograph being intended principally for the use of Geologists, we have 

 thought it advisable not to follow the Zoological classification of Corals in describing 

 the species belonging to the Fossil Fauna of Great Britain, but to distribute them in 

 reference to the different Formations in which they are found. We must, however, not 

 lose sight of the Natural arrangement of these Zoophytes, and before entering on the 

 specific history of the organic remains which we have to study, it is necessary that we 

 should make known to the reader the system of classification which we have adopted for 

 Polypi in general. The following Synopsis will suffice for that purpose, and will serve as 

 a sort of framework illustrative of the divers Zoological divisions to which we shall often 

 have to revert as we proceed in the descriptive part of our work. 



