f>2 



S. d.p. 47. Wood. G. C. p. 102. Turt. D. p. 

 103. Oval, convex, slightly contracted in the middle, 

 white or yellowish white and semi-transparent, with 

 obscure and rather remote longitudinal raised striae ; 

 beaks prominent, not quite central, teeth in one valve 

 obscure. Adhering to Echini by slender filaments. 



M. BIDENTATA. Turt. B.p. 60. MYA B. Mont. 

 44. t. 26. /. 5. Lin. Trans. 8. p. 41. Wood. 

 G. C. p. 99. D. p. 45. F. p. 465. Turt. C. D. 

 p. 102. Oval, sm >oth, rather produced at one end, 

 whitish, but not glossy, and frequently covered with a 

 rough coat; beaks nearer the broader end ; one of the 

 teeth oblique and spoon-shaped. $. in length. In 

 old oyster shells. 



M. FERRUGINEA. Turt. B.p. 60. MYA F. Mont, 

 p. 22. t. 26. /. 2. Wood. G. C. p. 100. D. p. 46. 

 Turt. C. D.p. 102. F. p. 465. Oblong, slightly 

 striated transversely, white, often covered or blotched 

 with an ochraceous coat ; bei;ks placed near one end, 

 obtuse ; one of the teeth in each valve erect, the other 

 much bent inwards and sloping downwards. ..... 

 Scotch and Western Coast. 



M. OBLONCA. Tvrt. B.p. 61. t. 11. /. 11. 12, 



