LETTER III. 

 To Thomas Pexnaxt, Esq. 



The fossil-shells of this district, and sorts of stone, 

 such as have fallen within my observation, must not 

 be passed over in silence. And first I must mention, 

 as a great curiosity, a specimen that was ploughed 

 up in the chalkv fields, near the side of the down, 

 and given to me for the singularity of its appear- 

 ance ; which, to an incurious eye, seems like a petri- 

 fied fish of about four inches long, the cardo (hinge) 

 passing for a head and mouth. It is in reality a 

 bivalve of the Linnaean genus of Mytilus, and the 

 species of Crista Galli ; called by Lister, Rastclluni ; 

 by Rumphius, Ostreiun plicatiini niiiius ; bv D'Argen- 

 ville, Aiiris porci. s. Crista Galli ; and bv those who 

 make collections, cock's comb. Though I applied to 

 several such in London, I never could meet with an 

 entire specimen ; nor could I ever find in books any 

 engraving from a perfect one. In the superb mu- 

 seum at Leicester House, permission was given me 

 to examine for this article ; and though I was disap- 

 pointed as to the fossil, I was highlv gratified with 

 the sigfht of several of the shells themselves in hiofh 

 preservation. This bivalve is only known to inhabit 

 the Indian Ocean, where it fixes itself to a zoophyte 

 known by the name Gorgonia. The curious foldings 

 of the suture, the one into the other, the alternate 



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