INTRODUCTION. Vil 
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 palaontologist 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 slow, 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 happens 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 palzontologists, 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. 
§ IIL. 
This Monograph bemg 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. 
