CO'iUGBYLlA—DITHYRjL 21. 61 



Mus. nost. Scotch and western coasts. 



Shell a quarter of an inch long, and nearly half an inch broad, 

 white, but often covered or blotched with an ochraceous coat, ob- 

 scurely wrinkled transversely : beaks placed near one end, obtuse ; 

 one of the teeth in each valve erect, the other much bent inwards 

 and sloping downwards. 



MoNTACUTA testa oblongd loevi dentibus erectis, oblonga. 



Shell oblong smooth, with all the teeth erect. 4- 



Tab. nost. 11, fig. Hand 12. 

 Mus. nost. From sand in Torbay. 



Shell resembling the last, but is about half the size, smooth or very 

 obscurely striate transversely, glossy. It has probably been over- 

 looked for a half-grown specimen of the former shell, but differs 

 essentially in having all the teeth erect. 



21. LEFTO^a. —TURTON. 



Testa compressa, suborbicularis, aquivalvis, wquilateralis, lateribus 

 subhiantibus. Cardo valvee alterius dente unico et laterali utrin- 

 quh lineari transverso ; alterius fovea media et dente utrinque 

 laterali transverso bipartite, segmentis ab umbone divaricatis. 

 Ligamentum internum. 



