170 



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. biangula, A. barbatula, A. angusta, A. interrupta, A. scapulina, A. qua- 

 drilatera. 



Shells of this genus are frequently found fossil in this island. One cast 

 from Bath seems to be of A. Note. 



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. Cucullaa. 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 

 cueullata of Chemnitz, Tom. vn. Tab. 53, Fig. 526528. 



