137 



does not strictly come within the province of the Con- 

 chologist, it has not as yet been otherways noticed in this 

 work : its strong resemblance to a bivalve shell, and its 

 importance as a distinguishing mark of particular strata, 

 have been inducements to the introduction of it. In 

 England it is found only in the Tetsworth or Weald 

 Clay and the sands below it, either in layers in the slaty 

 clay of the upper part of that formation, or dispersed in 

 the limestones and grit which occur in it. In France it 

 has been referred to the 2d fresh-water formation above 

 the chalk, and is accompanied by Paludinas and Cyrenae, 

 as in England ; — is it not possible that the places in France 

 where it has appeared, have not been enough examined, 

 and that if they were fully traced, they would prove to 

 belong to a formation analogous to the Tetsworth clay ? 

 for this fossil is not found above the chalk any where 

 near London or Paris. Professor Sedgwick was the 

 first person who noticed it in the Isle of Wight *, It 

 has lately been discovered by Dr. Fitton, to whose libe- 

 rality we are indebted for specimens from each of the lo- 

 calities ; — at HoUington near Hastings, where it occurs 

 in sand-stone along with a small Paludina and a Cyrena ; 

 in the Isle of Wight, either dispersed sparingly through 

 light-brown compact clay at Grange Chine, or in slaty 

 clayf (like the figure) in Sandown Bay, Chalk Bay, 



* Annals of Phil., new series. Vol. 3. p. 335. 

 f This Clay also occurs in Sussex. 



