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vi. “An Account of some remarkable Shells, found in | Cavities of 
a calcareous Stone called by the Stone-masons Plymouth-rag. 
By William George Maton, M.D. V.P.L.S. $c. and the Rev. 
Thomas Rackett, A.M. F.L.S. $c. With some additional Ob- 
servations relative to the Mytilus lithophagus, by Mr. James 
Sowerby, F.L.S. 
Read June 5, 1804. 
Tue specimen of the stone above alluded to, which was lately 
presented to the Linnean Society by Mr. James Sowerby, and 
which, from containing some shells that appeared to be of a 
doubtful species, was referred to us by the President for exa- 
- mination, is of a deep ashen hue, variegated with red, and con- 
tains a multitude of smooth regular cavities formed by Mytilus 
lithophagus. It was accidentally noticed by Mr. Sowerby, as it 
lay for the repair of aroad, in the suburbs of London. Making 
inquiries among the stone-masons in his neighbourhood, he was 
informed by them that it was brought from Plymouth: but this 
they seem to have inferred from no other circumstance besides its 
resemblance to a stone procured from a ridge of rocks in the vi- 
cinity of that town; and it has not been possible to ascertain 
positively whence it first came. After we have given some ac- 
count of the shells contained in it, there will appear a great im- 
probability of its being procured from any part of our own 
island, (unless indeed from some spot on the coast, where it may 
have been left after it had served the purpose of ballast,) for but 
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