sPH.ERimr. . 101 



It inhabits deep water, and is very frequently taken from codfish, 

 caught in Massachusetts Bay. On sandy bottoms, whole coast ; 

 Eastport in five fathoms ; Grand Manan, off Duck Island, four 

 fathoms sand (^Stimpson^ ; Salem Harbor (^Wheatland); Stoning- 

 ton (^Linsley^. 



There can be no doubt that this is identical with the British 

 shell, though the specimens 1 have seen are much smaller than the 

 foreign specimens usually are. 



I have arranged it under the genus Liicina, as most of its charac- 

 ters i)ertain to it, and none of them seem absolutely to forbid. The 

 genus Cryptodun has, however, been formed by Turton to embrace 

 this shell, on account of its single tooth. 



[Philippi has well shown that our species is quite different from 

 that of Europe above named. The marks he has designated are 

 sufficiently distinctive, viz. ours is much smaller, more oblique, the 

 hinder end on which the folds are situated is shorter, the lunule is 

 less deep, and the anterior margin is not concave, but rather con- 

 vex. Indeed the disparity in size and outline is so great as scarcely 

 to suggest a comparison. Having now seen large numbers agree- 

 ing in character, I must thus reverse my opinion. 



Family CYCLADIDzE, Woodward. 



Shell suborbicular, closed ; ligament external ; epidermis thick, 

 horny ; hinge with cardinal and marginal teeth ; pallial line sim- 

 ple, or very slightly inflected. Animal with open, simple mantle ; 

 siphons more or less united, orifices plain ; two unequal gills each 

 side ; foot large, tongue-shaped. 



Oeims SPII.ERIUITI, Scopoli. 1777. 



Shell small, thin, ovate-globose ; hinge with two minute cardinal 

 teeth in each valve, but sometimes in one only ; also compressed, 

 marginal teeth ; inlial lits fresh water. 



Sphserium simile. 



Fig. 53. 



Shell oval, truncated at the extremities in young, and rounded in adult speci- 

 mens, convex, sub-equipartite ; beaks shghtly elevated ; surface with conspicu- 

 ous concentric wrinkles ; epidermis dark chestnut-brown. 



