39 
ierior extremity, which is separated by a ridge 
from the middle; posterior extremity produced, 
rounded, gaping ; section obovate. 
Shell very gibbose, wider than long, with prominent 
beaks, and the anterior portion almost flat and without 
ribs. Hitherto found only at Bognor: Mr. Dixon has 
several specimens in his cabinet besides the one figured. 
PHOLADOMYA margaritacea. 
TAB. DC XXX.— Jig. 3. 
Spec. Char. Subquadrate, very convex, ribbed; 
ribs small, few (about 12), extending over the 
small anterior portion of the surface, which is 
separated by an angle from the middle ; beaks 
produced, pointed, placed near the anterior, 
almost straight, truncated extremity ; section 
elliptical. 
Syn. Cardita margaritacea, M. C. 1. 175. Jig. 2&3. 
Pholadomya margaritacea, M. C. General Index. 
Morris, Cat. 98. 
1 wo new species of Pholadomya having been found in the 
London Clay, it has become necessary to describe the P. 
margaritacea with more precision ; and thus we have been 
