14 
the posterior side and part of the front. The posterior 
side is very concave, and separated by an obtuse ridge. 
The substance is very thin, except that of the hinge, 
which is strong. 
This shell is abundant in the sandstone, called in 
Devonshire, Whetstone: it is mentioned by Parkinson in 
his dd Vol. p. 226. I have received it in various stages 
of growth from my kind and amiable correspondent, 
Miss E. Hill. 
CORBULA levigata. 
TAB. CCIX.---Figs. 1 and 2. 
Spec. Cuar. Orbicular, gibbose, smooth, and 
thin; beaks prominent, incurved. 
A. very smooth regularly convex thin shell, scarcely 
wider than long. I have only seen one, that is the 
smaller valve, and only an imperfect specimen of that ; 
but it shews the hinge, in which it exactly agrees with 
C. gigantea. The tooth in this valve in both these spe- 
cies is situated upon the posterior edge of the pit that 
receives the tooth of the other valve, in which they differ 
from other Corbule, although in some of them there are 
traces of such a disposition. 
From Black Down, by favour of Miss E. Hill. 
CORBULA globosa. 
TAB. CCIX.---Fig. 3. 
Spec. Cuar. Globose, smooth; anterior side of 
the larger valve produced into a lip; trun- 
cated ; beaks equal. 
A. very small shell, equal én thickness to its length ; 
ithe posterior side is round, the anterior obscurely trun- 
