A MONOGRAPH 



OF THE 



BRITISH CARBONIPEROUS LAMELLIBEANCHIATA. 



INTRODUCTION. 



No systematic work on British Carboniferous Lamellibrancliiata lias been 

 attempted since the publication of M'Coy's two great works in 1844 and 1851-6. 

 Since then systematic conchology has greatly advanced, and, at the same time, 

 palseontological mateinal has been accumulated to a very large extent ; fortunately, 

 too, in many cases specimens or fragments have been obtained in special states of 

 preservation, which have demonstrated the characters of the hinge-structure and 

 the position of muscle-scars, and the character of the pallial line — features which, 

 in the necessary absence of the soft parts of the animal, are made use of as a 

 basis of conchological classification. Owing to the fact of the preservation of 

 these essential characters, many changes have been found necessary in the generic 

 nomenclature ; and will be adopted in the following Monograph. 



The study of the bivalve shells of the Carboniferous age has been largely carried 

 on, both in Belgium and North America, by learned and competent observers, 

 consequently much uncertainty has been caused by such independent and widely 

 separated research, authors being unwilling, in the absence of specimens, to admit 

 that the same species had a world-wide distribution ; and the result has been that, 

 both generically and specifically, a large synonymy has been created. 



In nearly every case the older palaeontologists named their specimens from the 

 observation of external characters only, and often from a supply of specimens 

 too limited to ascertain the real type of a genus or species ; and it has generally 

 been the rule to regard the survival of genera and species as altogether limited to 

 those periods adopted for the purposes of stratigraphical classification, and to 

 hesitate to recognise the same form in the beds of two or more diflFerent epochs. 



The all but universal acceptance, by working conchologists, of the Darwinian 

 theory of evolution by variation has to a large extent changed the views which 

 older observers held on the permanence of species. It may be now regarded as an 



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