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not often find the actual remains in the Coal formation, we 

 conceive it very proper to give a figure, especially as the 

 shells are in such perfection as to be known outwardly 

 nearly as well as if they were recent. As far as I could 

 detach the coaly matter, &c. from the inside of one, it 

 seemed to have no more hinge than Mytilus cygneus of 

 Linnaeus, which it greatly resembles, but it is a thicker 

 shell : it does not strictly accord with any modern one that 

 I know, I shall therefore call it Mytilus crassus. The shells 

 are composed of crystallized Carbonate of Lime, in some 

 parts rather transparent. The specimen has other Carbonate 

 of Lime in the crossings and small partings, with some 

 argillaceous Oxide of Iron. The coaly part is mostly bi- 

 tuminous, and has the fractures corresponding with it. It 

 appears to be found in large compressed layers, with innu- 

 merable quantities of shells of this sort only. They were 

 called petrified Oysters by the miners, who found them in a 

 stratum above the Cannel Coal near Wigan. 



I at present know of no others so absolutely in Coal. The 

 usual Ironstone that accompanies Coal has many species 

 of shells, which however seem to accord with the Mya of 

 Linnaeus. 



