40 
led to the discovery of a fourth species, the subject of the 
next description. P. margaritacea is to be known from 
both the preceding species by its length and square form ; 
it is often so crushed as to resemble Cardium Cardissa in 
shape, when the beaks become remarkably pointed. It was 
found abundantly in the lower part of the London Clay at 
Chalk Fa rm, while the excavation for the Birmingham 
railroad was proceeding : it is also common on the Isle of 
Wight, whence the remarkably perfect specimen, figured 
on the present plate, was obtained for me by Professor 
Morton. It also occurs at Brentford and at Bognor, and 
was found in a well at Richmond, as formerly stated. 
PHOLADOMYA ? cuneata. 
TAB. DCXXX.— fig. 4. 
Spec. Char. Trigonal, concentrically striated, 
posteriorly wedge-shaped ; the anterior side 
cordiform, nearly flat, obscurely ribbed, its 
margin raised and reflected over the beaks ; 
length and breadth about equal. 
Syn. Cardita margaritacea, M. C. 297. f. 1. 
Pholadomya cuneata, Morris , Cat. 97. 
A small species approaching very nearly to the genus 
Pholas, having thin sharp lines upon its surface, with the 
anterior side extremely short, and gaping when young; 
the peculiar elevation of the anterior portion of the hinge 
line, which is reflected over the beaks, also favours the re- 
semblance to P/iolas ; the pallial impression is remarkably 
strong and rough. Found only at Pegwell Bay near 
Ramsgate (called Bogwell Bay in the description of plate 
297). This shell was formerly confounded with P. marga- 
ritacea, but the discovery of more perfect specimens, with 
the anterior margin reflected between and over the beaks, 
has proved it to be quite a different thing. 
