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DESCRIPTIYE PART. 
DESCRIPTION OF THE GENERA AND SPECIES OF AMMONITES. 
Before commencing a description of the genera and species of Ammonites figured 
in the plates of this work I desire to express a few thoughts by way of introduction to 
the study of species. First, with regard to the method I intend to pursue in the 
execution of this rather arduous duty, it is my intention to adopt the same lines I 
laid down and steadily followed in the description of the Jurassic and Cretaceous Echino- 
dermata already published in the volumes of the Palseontographical Society. 
In the systematic part of this work I have shown the student the importance of a 
more accurate and exhaustive study of the Ammonite shell than has hitherto been 
accorded to it by the majority of ordinary observers, and have proved how necessary a 
correct knowledge of all its essential features is in order to understand thoroughly the 
affinities of a species. I intend, therefore, to give a very full account of the characters 
of the different genera as they come in succession before us in the sequel. 
The description of an old species necessarily implies a careful scrutiny of the 
synonyms by which it has been known and noted by former observers. This section of 
my work requires very careful study and much research, and should I succeed in clearing 
away some of the difficulties which surround the synonymy of the Ammonites I have so 
long studied, it will, I venture to hope, prove to be not labour in vain. The study of 
the Ammonite shell has shown us how very much many of these extinct Molluscs have 
changed their forms during the different phases of their lives, and how often species have 
been described and figured as new which afterwards were found to be only the transient 
conditions of some other well-known form. This is one of the errors that has greatly 
complicated the study of the synonymy of many species, and rendered the subject often 
so complex and difficult that we can scarcely hope to avoid errors in our attempts to 
unravel the true form of a doubtful species. It has only been by collecting specimens 
for the last thirty years which represent the young, middle-aged, and adult condition 
of as many species as I could obtain, that I have slowly learned how to solve some of 
the complex problems I have encountered, to my own satisfaction, and, I venture to hope, 
to that of the readers of this Monograph after my demonstrations shall have been made ; 
