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teeth ;—in that it is a right angle,—in this it is greater. 
The lunette of the recent one is regularly convex ; in 
the fossil it is depressed in the middle, and also lies 
deeper. The fossil is generally less convex than the 
recent, and a trifle wider. The striz in both are beneath 
the surface, except near the crenulated edge: in the fos- 
sil they are most conspicuous in old shells. 
Found in Barton Cliff: the small specimens (figs. 3 
and 4), are from Highgate: whether the latter, (fig. 4) 
should be considered as a distinct species, or only a va- 
riety, it is not perfect enough to determine: the strie 
upon it are elevated over nearly the whole surface not 
confined to the margin. 
Lamarck and Brocchi having declared didir shells to 
be identical with the Linnean A. nucleus, in conformity 
with the general opinion respecting these fossils, I have 
added a query to their synonima, for I have not seer 
foreign specimens, and they may prove to be different 
from either of the Hampshire ones, (N. similis and tri- 
gona,) which have also been confounded together. 
NUCULA trigona. 
TAB. CXCII.---Fig. 5. 
Spec. Cuar. Ovato-deltcid, compressed, smooth; 
edge crenulated ; hinge-pit short; lunette 
concave. . 
Disrinevisuzp from N. similis by its triangular form, 
flatted valves, and concave lunette, which also distin- 
guishes it from A. nucleus of Linnzus. 
Sent me along with N. similis from Barton, by Miss 
Salisbury : it appears to be quite new. I would propose 
to call the A. nucleus of Linn. Nucula intermedia, be- 
cause it comes between this and N. similis in form, as 
the hinge of this is more acute than a right angle. 
