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 silicized 
state. 
EE 
CARDIUM umbonatum. 
TAB. CLVL.---Fig.-2, 3, and 4. 
Spec. Cuar. Orbicular, gibbous, nearly equilate- 
ral, longitudinally striated and obscurely cos- 
tated; anterior edge concaye, and angular 
above. 
LLeneru and breadth three-fourths of an inch; the 
costz are so little elevated that the edge is nearly entire, 
but 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, E 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. 
