246 ARCA. 



angulated teeth, with the angular sides placed towards the 

 umbo, and is very nearly allied to A. rostrata, but is much 

 narrower in proportion to the length. 



tenuis. 45. Shell somewhat heart-shaped, smooth; 

 umbones small, with the summits slightly in- 

 flected, and placed near to one end ; margin 

 entire. 



Area tenuis. Montagu Supp. p. 56. t. 29. f. 1 . 



Inhabits the Sea in Dunbar and Leith Roads. Laskey. 



Shell hardly a quarter of an inch long, and the breadth but very 

 little exceeds the length ; it is white, covered with an oliva- 

 ceous epidermis, and the inside is somewhat pearly. Mr. 

 Montagu says, the hinge is pectinated with about fifteen 

 elevated teeth placed within the margin, six on one side and 

 nine on the other, divided by a small concave plate that pro- 

 jects forwards. 



