C T 47 ]-: 
Copping or Height of the Apexx > r upper Part. Thi* 
Foffil alfo confifts of a hard ftony arenaceous Sub- 
ftancc like the other. 
From the Infpedion of the feveral Hollows of 
thcfe Echinites , it is evident they were not imme- 
diately moulded in the Shells, but were fo m'd in 
Cavities which thofe Shells formerly filled in the 
Rocks they were lodged in. The Rocks were appa- 
rently of a loofened arenaceousTexture, and the Water 
&c. continually pervading them, rotted and deftroy’d 
the inclofed Shells, and bore away their whole Sub- 
ftance. In the fame manner, and by the fame means, 
were the ftony. Particles replaced into thofe very Ca- 
vities which the Shells formerly filled ; conlequently 
thcfe Bodies were moulded cxadly to the faid 
Cavities. 
This Remark carries a Conclufion with it, if Ob* 
fervation be made, that the Hollows and fol id Parts 
of thefe Stones exadly anfwer to the Hollows and 
folid Parts of the very Shells themfclves ; which, had 
they been moulded in the very Shells* muft have 
happen’d diredly contrary; the folid Parts of the 
Shells forming Hollows in the Stone, and vice verj'a. 
In all fandy or lax earthy Matter fofiil Shells are very 
feldom found, but only the moulded Stones ; the 
loofc Texture of thofe Subftances giving freeAccefs 
to Wafer, Vapours, and mineral Exhalations, 
which intirely corrode and deftroy the Shells buried 
in it. 
I have taken the Liberty to produce before the 
Society a recent Echinus of this Genus from the 
Weft bidies , to elucidate my Subjed ; as alfo two 
Drawings done by Mr. Mynde ; viz. of the Bafis of 
T 2 the 
