56 



a lens are found to be acute ridges, flightly refle<5led ; on 

 the upper part from the umbo to the roftrated end the /In'a 

 are difcordant, making an abrupt angulated turn acrofs 

 feveral flight longitudinal ribs, with which that part alone is 

 furniflied. The infide is of exquifite polifh, and the margin 

 plain : the teeth are numerous on each fide the beak, divided 

 at that part by a depreflion void of denticulations ; thefe teeth 

 are angulated, each feries formed with their angular fides 

 towards the centre. Length half an inch ; breadth three 

 quarters. 



Although this rare and elegant fpecies of Ark has been 

 defcribed as an inhabitant of the J^ortvegian and Baltic feas, 

 it had never been fuppofed to inhabit the coafl; of Great Bri- 

 tain ; but from the undoubted authority of Mr. Laskey we 

 are enabled to add it to the catalogue of indigenous Ihells. 

 Several fingle valves and one live fpecimen were taken in 

 the dredge by that gentleman in Scotland, off St. Abb's head. 

 It is ufually defcribed to be covered with agreenifli fkin, pro- 

 bably fomething foreign to the fliell, as the Britijh fpecimen 

 in quefiion was perl"e6l, and in high prefervation, but defii- 

 tute of any fuch covering as the reprefentation of the figure 

 given will evince. 



Tenuis. Shell fub-cordate, fmooth, white, covered with an oliva- 



Tab. 39- f. 1 ceous epidermis : umbo very Imall ; beaks flightly inflecSted, 



and placed near to one end. infide fmooth, white, and 



fomewhat nacred ; margin thin and intire : hinge pe(5linated 



with 



