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 Farm, 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. "DQXXX.—jig. 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. 2^1. f. 1. 

 Pholadomya cuneata, Morris, Cat. 97. 



A SMALL species approaching very nearly to the genus 

 P/iolos, 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. 



