170 
In the whetstone sand-pits, at Blackdown, a small species of this ge- 
nus is found, in which the shell is very thick, and the teeth of the hinge 
few and large. These pectunculi, with several of which I have been 
favoured by the Rev. Mr. Cleeve and Mr. Clarke, are so much impreg- 
nated with silex, that some of them possess a considerable degree of 
transparency. 
XCIX. Area. A transverse inequilateral shell : the beaks distant ; 
the hinge with many teeth, disposed in a straight line ; the teeth lamel- 
lated, close, and alternately inserted between each other : a subrhom- 
boidal smooth area between the beaks, on which the cartilage was disposed. 
These are marine shells ; and are easily recognised by their general 
form. They frequently gape along their superior edge, and have two 
marks of attachment on each valve. Lamarck particularizes seven spe- 
cies, which are found fossil in the neighbourhood of Paris : 
A. diluvii. A. barbatula. A. interrupta. A quadrilatera. 
A. biangula. A. angusta. A. scapulina. 
Shells of this genus are frequently found fossil in this island. One 
cast from Bath seems to be of A. noce. 
At Plate XI. Fig. 29, is represented an ark of an uncommon form, 
the valves terminating in an alated form. This is a German fossil, and 
is attached to some oysters, with serrated margins : a sufficient portion 
is, however, visible, to allow of the drawing to have been fairly taken, 
although not sufficient to allow of particularizing its specific characters. 
C. Cucullcea. A nearly transverse, inequilateral, ventricose bivalve, 
with distant beaks : the hinge formed of many teeth, disposed in a 
right line, and terminated at each end by three or four transverse 
parallel teeth : a flat and sulcated area, for the reception of the car- 
tilage. 
The shells of this genus differ from the arks, in the teeth at the end of 
the hinge, which are placed in a transverse direction, directly contrary 
to that in which the row of small lamelliform teeth are disposed. Area 
cucullata of Chemnitz, Tom. vn. Tab. 53, Fig. 526 528. 
