256 INVERTEBRATA OF MASSACHUSETTS. 



leaves of Laminaria. They were received by Leach and Beck 

 from Greenland, Baffin's Bay, and the Arctic Seas. I have ob- 

 tained them of a much larger size than is given by any other 

 observer. 



It is a very pretty shell, generally iridescent, or reflecting a metallic, 

 bronze lustre. It has more the aspect of a land or fresh-water shell, 

 than that of a sea shell. It is not likely to be confounded with any 

 other species except the following. 



I have given this species as die M. urclica, Leach, in accordance 

 with the opinion of Mr. Sowerby, who compared our shells with the 

 authentic specimens in the British Museum. 



I must confess, also, that in comparing the descriptions of M. vul- 

 garis and M. drctica in the " Malac. and Conch. Magazine," and 

 specimens of M. vulgaris^ sent me by Mr. Sowerby with small speci- 

 mens of the above described shell, I can perceive no essential disdnc- 

 tion, excepdng in size ; the first is said to be palish, the second oliva- 

 ceous. 



Margari'ta argenta'ta. 



Shell deprcsscd-conicul-y of a jiearly-xvliitc color, covered loith 

 microscopic, revolving linen ; umbilicatcd. 



Figure 164. 

 - State Coll., No. 35. Soc. Cab., No. 2412. 



Shell minute, conical, with an obtuse tip, of a dead pearly- 

 white color ; composed of four convex whorls, the last of which 

 is very slightly angular ; the next above is elevated, but the up- 

 permost, and frequently the two uppermost, are not elevated above 

 the succeeding whorl, so that the apex is obtuse ; everywhere 

 covered with crowded and very fine revolving lines ; suture deep; 

 aperture circular ; lip sharp, simple ; interior pearly and irides- 

 cent ; umbilicus moderately large. Length -^^ inch, breadth | 

 inch. 



Found in fishes caught off Cape Ann, and Cohasset, in consid- 

 erable numbers. 



