128 
this action has taken place is of an hard or harsh gritty 
feel, with particles of Mica ; the whole more or less con- 
creted. These and other shells I have, and shall occa- 
sionally show are very abundant in it, all in a silidzed 
state. 
CARDITJM nmbonatum, 
TAB, CLVI. — Fig. 2 , 3, and 4. 
Spec. Char. Orbicular, gibbous, nearly equilate- 
ral, longitudinally striated and obscurely cos- 
tated ; anterior edge concave, and angular 
above. 
JLength and breadth three-fourths of an inch ; the 
cost® are so little elevated that the edge is nearly entire, 
hut the margin is strongly toothed within ; the anterior 
side is separated by a concavity, so that the upper angle 
of it forms a sort of boss ; it was formerly thought to be 
the young of our common Cockle, Cardium edule ; the 
evenness of the contour and the concavity around the 
anterior side will, I trust, always distinguish it, with 
very little difficulty. 
Also from Blackdown and silicized : very neat speci- 
mens frequently occur. Fig. 4 shows an accidental canal 
of which there are slight vestiges in several specimens. 
