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 Paludinae 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 Hollington 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 
clay f (like the figure) in Sandown Bay, Chalk Bay, 
* Annals of Phil., new series. Vol. 3. p. 335. 
f This Clay also occurs in Sussex. 
