Class VI. ARCA. ARK-SHELL. 



GENUS XIII. ARCA. ARK-SHELL, 



Animal, a Tethi/s. - - ■ 



Shell equivalve. 



Teeth of the hinge numerous, inserted between 

 each other. 



* With the edge entire ; beaks inflected. 



Lin. Syst. 1140. No. 16q. Mytilus. Maithiol. apud DioS' l. mom. 



Gm. Lin. 3306. cor. lib. ii. c. 5. p. 301. distorted. 



Borlase's Nat. Hist. Cornw. Lin. Tr. viii. gi. 



tah. xxviii. fg. 15, l6. Mont. Test. Br. ISQ. t. 4./. 3. 



List. Conch, tah. 368. A. tortuosa. Br. Zool. iv. 97. 



A, with a rhomboid shell, deeply striated from 

 the apex to the edges ; breadth half an inch. 



Inhabits Cornwall; found also near Wey- 

 mouth; extremely rare. 



Mont. Test. Br. Sup. 51. 2. FU3CA, 



* A. with a finely reticulated shell, of an uni- 

 form purplish brown color, destitute of any 

 colored bands ; length three quarters of an 

 inch, breadth an inch and a half. 



Found in Devonshire, Cornwall, and Scot- 

 land. 



