148 
ISOCARDIA oblonga. 
TAB. CCCCXCI. —Jig. 2. 
Spec. Char. Oblongs anteriorly expanded^ smooth ; 
posterior side very small, the beaks curved into 
it ; hinge line nearly straight. 
This is a transversely oblong shell, whose margin is 
four-sided, the side beneath the beaks is very short 
and much curved, the others long, and approaching to 
straight ; it is very gibbose towards the beaks; the shell 
is very thin. 
Found rather sparingly in the Black Rock, near Dub- 
lin, from two to four inches wide. It is a boldly formed 
fossil, and the specimens are generally very regular and 
well defined ; none, however, have been met with that 
show enough of the hinge to prove by it that they belong 
to the genus Isocardia ; — the same observation will also 
apply to the I. concentrica it is only by their general 
form that we are led to arrange them both under that 
genus, the thinness of their shells is rather an objection. 
An Isocardia exactly resembling the Cor is met with 
in the Crag, and we have the cast of another very similar 
in Limestone ; but neither, perfect enough for figuring. 
