78 PECTIXID.E. 



its own. This remarkable construction is funnel-shaped 

 with the larger end contracted, and sufficiently wide to 

 admit of the Lima moving freely up and down, but not 

 turning round in it. Here it lives, secure from prowl- 

 ing fish and crabs. The case is lined inside with a 

 closely-woven net of byssal threads, plastered over with 

 slime or excrement. This smooth and soft lining con- 

 tains a quantity of Diatom-cells, and yields a rich 

 harvest to those who collect these exquisite organisms 

 for microscopical examination. Such remains of per- 

 petual feasts remind one of the similar exuviae which are 

 found at the bottom of a spider's web. No species of 

 Lima is noticed in Dr. Gould's ' Invertebrata of Massa- 

 chusetts/ or in any other work on the conchology of 

 the United States ; nor has Dr. Philip Carpenter, in his 

 elaborate list of the Mollusca inhabiting the north-west 

 coast of America, enumerated any as belonging to the 

 northern fauna of that extensive district. 



The very ancient genus Plagiostomus of Lhwyd (P/«- 

 giostoma of Sowerby's f Mineral Conchology ') is con- 

 sidered by some palaeontologists to be identical with the 

 present genus. It may be connected with it through 

 the genus Limea of Bronn, and form a passage to Spon- 

 dylus. Poli used the name Glaucus for the animal of 

 the present genus. 



A. Shell equilateral, with a straight outline. 



1. Lima Sar'sii*, Loven. 



Limea Sarsii, Lov. Ind. Moll. Scand. p. 32. 



Body milk-white : mantle set with large, thick, and ringed, 

 but not numerous cirri or tentacles. 



Shell roundish-oval, slightly oblique, convex, rather solid 



* Named in honour of Professor Sars. an eminent Norwegian zoologist. 



