95: 
ARCA. 
Gen. Coan. A transverse inequilateral bivalve, 
the beaks distant, hinge with many teeth, dis- 
posed in a straight line; the teeth lamellated, 
close, and alternately inserted between each 
other: a subrhomboidal smooth area between 
the beaks, on which the cartilage is disposed. 
~ ARCA subacuta. 
TAB. XLIV.—Upper figure. 
Spec. Cuar. Gibbose, margin an obtuse scalene 
triangle deeply plaited; breadth grater than 
the length, surface longitudinally striated. } 
Tur hinge extends nearly the whole width of the shell, 
forming the longest side of the triangular margin; the teeth 
are sharp and numerous; the marginal plaits are rounded 
and very deep, particularly at the anterior side, they are 
‘elongated over the surface of the shell, at least I presume 
so from the impression of the inside, which is all I have to 
examine. 
This happens to show the nature of the hinge teeth ex- 
ternally, else it might have been considered as a Cucullea, 
a division or genus of Lamarcke’s taken out of the Arca of 
Linn. and on which the teeth are on a line parallel with the 
hinge, and which I shall have an opportunity to show here- 
after. It is little else than the chalky remains of the shell 
covering a hardish Limestone Marle. From Sussex, by 
favour of Mr. Mantell. - 
