175 
C AUDIT A margaritacea. 
TAB. CCXCVIL— 1, 2, and 3, 
Spec. Char. Transversely obovate, gibbose, with 
an obscure longitudinal keel and several small 
ridges, concentrically undulated,, pearly within ; 
anterior side slightly produced, posterior very 
short, convex. 
The only pearly Cardita with which I am acquainted: it 
is a thin rugged shell somewhat wider than long, the 
anterior side probably gapes a little ; the beaks are 
prominent, much incurved, and have a considerable hollow 
beneath them ; the posterior side is distinguished from 
the rest of the shell, by an obtuse keel or angle ; the 
longitudinal ridges are very variable in number, they 
are crossed by rugged undulations and lines of growth. 
A shell characteristic of the lower part of the London 
Clay. I have it from a well dug on the top of Richmond 
Hill, where it was brought up from the depth of 265 
feet. Fig. 1 represents a very perfect specimen from 
Bogwell Bay, in the Isle of Thanet, given me by the 
late lamented Lady Wilson ; Fig. 2 was given me by 
Mr. Sutton, who obtained it at Brentford. Fig. 3 is 
from a specimen collected in the dark coloured (London) 
Clay, next to the red Clay in Alum Bay, on the Isle of 
Wight, by Abraham Clarke, Esq. of Carisbrooke ; they 
are all extremely tender, and variously compressed ; 
some are mixed with Pyrites. 
