88 
stress has been laid, is too variable, as we have just seen 
in the genus Corbula at tab. 362, to be relied upon ; and 
an examination of the recent species is still wanting to 
establish the two other points : the erosion of the um- 
bones does not occur in the other fossil species. 
First observed by Mr. Webster (Trans. Soc. Geol. VII. 
p. 227), and again by Mr. G. B. Sowerby, who has com- 
pared it to Mya labiata (Annals of Phil, new series, Vol. 
II. p. 220). They found it near the top of Headon Hill : 
Prof. Sedgwick has since found it at Calbourne ; and it 
probably occurs near the top of the upper fresh-water 
formation on other parts of the Isle of Wight. 
MYA arenaria. 
TAB. CCCLXIV. 
Spec. Char. Ovate, anteriorly rather pointed, 
posteriorly rounded ; hinge tooth large, 
with a lateral appendage. 
Mya arenaria. Linn, et Auctorum . 
So perfectly does this resemble the recent Mya arenaria, 
that we can find no distinguishing mark. Tn all proba- 
bility this is one of the few shells belonging to genuine 
diluvian deposits, and accidentally mixed with the older 
fossils. It is frequently found, but rarely perfect, in the 
Crag pits of Norfolk and Suffolk. I first received it 
from Mrs. Cobbold of Ipswich. The figures are taken 
from specimens in the possession of the Rev. G. R. 
Leathes. 
