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In adopting the name Gryphaea, we do not lose sight of the fact, 

 that in all probability, the inhabitants of the shells to which it is 

 restricted were true oysters ; but there is connected with it, so well 

 defined an idea of an oyster of peculiar type, which first makes its 

 appearance in the Liassic formation, that the convenience of its 

 retention is obvious, and the question whether it should take generic 

 or sub-generic rank, is of trifling importance. This group of shells 

 consists of those which, from regularity of form, uniformity of 

 character, and presumed difference of habit, were separated from the 

 oysters under the name of Gryphaea, by Lamarck, in his " Systeme 

 des Animaux sans Vertebres," in 1801, but as he was apparently 

 misled, by having studied the adult shell only, and conceiving that 

 it had always been free, therefore gave in his generic definition 

 undue prominence to this assumed fact, we adopt the following 

 description of Sowerby, from his Mineral Conchology, as generally, 

 though not absolutely, more concise and correct. 



GRYPH^A. 



" A free, (except when very young,) unequal-valved, inequilateral 

 "bivalve, larger valve involutely curved, concave, smaller valve flattish, 

 " beakless ; hinge, a transversely striated pit, containing an internal 

 "ligament, without teeth or crenatures." 



The Liassic species, recognised by most English writers, to which 

 the foregoing generic terms apply, are those to which we have now to 

 address ourselves, and may be stated as follows : — 



Gryphaea incurva, SoAverby. 



G. suilla, Schlotheim. 



G. obliquata, Sowerby. 



G. Maccullochii, Sowerby. 



G, depressa, Phillips. 



G. cymbium, Lamarck, 

 all of which, labelled as above, are to be found in most collections of 

 importance throughout the kingdom, and are more or less common (as 

 we believe) in this district. 



Upon enquiring where, as tyros, we may find pictorial illustrations 

 of the differences between them, we learn that we must refer to the 

 works cited as follows : — 



For G. cymbium, to the Encyclopedic Methodique ; the Petrefacta 

 Germanias of Goldfuss ; the Coquilles Fossiles des Environs de 

 Paris, of Deshayes; Sowerby 's Mineral Conchology ; or Phillips' 

 Geology of Yorkshire. 



For G. depressa, to the last-named work. 



