%%\ M\RINE SHELL9 



inclosing small irregularly oval, white, or yellowish- 

 white spots. They sometimes however, are of a uni- 

 form greenish or brownish colour. Several speci- 

 mens of this species were communicated to me by 

 Mr. Aaron Stone, who found them on the coast of 

 Maine. 



FISSURELLA, Lam. 



Species. 



F. *alternata. Shell oblong-ovate, moderately 

 thick, cinereous or dusky, with equal concentric lines, 

 crossed by alternately larger and smaller radii, all 

 which are equable or not dilated in any part ; vertex 

 placed nearer the smaller end ; perforation oblique, 

 oblong and a little contracted in the middle ; within 

 white ; margin simply crenate ; apex with an in- 

 dented transverse line at the larger end of the perfo- 

 ration. 



Length four-fifths of an inch. 



Breadth three-fifths. 



Height more than two-fifths. 



Inhabits the coast of the United States. 



Cabinet of the Academy, and Philadelphia Mu- 

 seum. 



Bears a general resemblance in its sculpture to 

 F. Grceca, but the radii are not dilated at the points 

 where they are crossed by the concentric lines. I 

 have specimens from the coast of Maryland that 

 measure one inch and a half in length. 



