40 



M. TRXJNCATA. Lin 1111. D. p. 42. Lam. 1. 

 Ch. f. 1, 2. Don. t. 92. Pen. t. 41. f. 14. 

 Mont. p. 32. Turt. B. p. cl.F. p. 463. Ovate, 

 ventricose, truncated anteriorly, rounded posteriorly, 

 ventral edge nearly straight ; dull white under a tough 

 yellowish wrinkled cuticle, marked with coarse striae of 

 growth: tooth rounded obtuse entire and projecting 

 forwards. 2... 2,5. Common in chalk. 



M. ARENAIUA. Lin. 1112. D.p. 42. Lam. 2. 

 Ch.f. 3,4. Don. t. 85. Pen. p. 79. t. 42. F. p. 

 463. Mont. p. 30. Turt. B.p.32. M. AcuTAand 

 MERCENARIA. Say. Ovate, rounded at both extremi- 

 ties but slightly attenuated and produced anteriorly, 

 convex, thick, dull white under a wrinkled brown epi- 

 dermis; inside glossy white; hinge composed of a 

 rounded projecting tooth and a smaller acute one by its 

 side. 3... 5,5. Common. 



M. NVREGICA. Turt. Lin. t. 4. p. 178. M.STRI- 

 ATA. Mont. Lin. T. 11. p. 188. t. 13. / 1. LYONSIA 

 S. Turt. B. p. 35. t. 3./. 6, l.F.p. 463. Oblong, 

 thin, equivalve, semi-transparent, pearly white under a 

 brownish epidermis, rounded at one end, waved and 

 truncated at the other; tooth not fixed. ...!. Rare. 



