of the Isle of Wight. 283 



Sow. We had considered it as a new Modiola, on account 

 of an undulation wliich the salient angle of each valve pi'esents, 

 a character which is not seen in the species of Sowerby, which 

 is besides more rounded at its inferior extremity. 



AmpuUaria Icuvigata, Desh. — This species, which, accord- 

 ing to M. Deshayes, is indeed an AmpuUaria^ and not a Na- 

 tica, is assimilated in the list of Mr. Forbes to a Natica ro~ 

 tundata, which we have not been able to compare with it, not 

 knowing where to find a figure or a description of it. 



In the face of these facts, which every one can verify, we 

 are in the unpleasant alternative of either charging Mr. E. 

 Forbes with having made these determinations too hastily, or 

 of considering the plates of Sowerby so bad that it would 

 henceforth be wholly impossible to use them. In this latter 

 case, which does not seem to us to be the most probable, it 

 would be just, in correcting our errors, to declare that they 

 were indispensable in the state of things, in order not to let 

 a suspicion of levity fall upon us which we had taken every 

 means to avoid. 



It will be supposed, from the preceding statements, that we 

 entertained some doubts on the whole of the names which 

 compose the lists on which Dr. Fitton relies. We cannot 

 admit, for example, that our Exogyra aquilina, which is a va- 

 riety of the Exogyra subsinuata or Couloni, can be considered 

 as belonging to the Exogyra sinuata, which differs much from 

 the preceding both in form and position. Nor do we think 

 that the small smooth Exogyra which Sowerby has figured 

 under the name of Gryphcca Iccvigata^ can represent the ExO' 

 gyra Couloni (our Exogyra subsmuata), the surface of which 

 is always more or less covered with varices, knots and other 

 irregularities. It is very difficult to believe also, with Mr. 

 Forbes, that the Trigonia caudata, Agass., can be assimilated 

 to the Ttngonia scabra^ Lam. 



With these restrictions, the lists in question present but a 

 small number of truly Neocomian species, and thence the con- 

 clusions which Dr. Fitton has drawn from them lose their force. 



For our part, these conclusions would not appear to us 

 necessary even had there been no error in the lists of Mr. 

 Forbes, and we are even of opinion that, notwithstanding the 

 interesting discoveries which have just been remarked, the 

 Neocomian formation represents the Weald Clay of England. 



Although we have stated in our Memoir on the Chalk For- 

 mation of the Aube the principal reasons which have led us 

 to admit this last assimilation, the first idea of which is due, 

 indeed, to Elie de Beaumont, it will not be useless to recall 



