C 433 ] 
fparry Matter, formed within the Shell of the Echi- 
nus, and taking their Figure thence as in a Mould : 
Which Shell is oftentimes broken off and gone, but 
remains at other times impregnated with talcy or 
fparry Particles: Whereas the Subjedt now laid be- 
fore us is compofed of a tranfparent cryftalline Sub- 
ftance, which has received its general Figure by hav- 
ing been circumfcribed within the Shell of fome 
Echinus, and fhews linear Ridges andDivifions corre- 
lpcndent to the Lines and Plates found in this kind of 
Echinus . 
Was this all, it would be a very uncommon Pro- 
du&ion, as thefe Bodies have been very rarely known 
to be formed of Cryftal * 5 but it is render'd much 
more curious and extraordinary, by having exadt 
Rows and Series of little Cells, all of the fame re- 
gular Figure, though leffening gradually in Size, as 
they afcend from the Bafe upwards. ( Vide Fig. 3; 
This Body having been formed within the Shell 
of an Echinus , one would expeft (as is the Cafe im 
all other Echinitce ufually known), that its Figure 
fliould be exa&ly anfwerable to the Mould wherein 
it was formed ; but Mr. Baker begs Leave to take 
notice, that the Echinus 9 Shell is perfedtly fmooth 
internally, having no rifing Parts correfpondent to 
thefe Cells or Cavities; and therefore, as it could 
not receive its Configuration from thence, it muft 
be owing to the natural Shooting of the cryftalline 
Matter 
* Sir Hans Sloane has a Mafs, which was form’d within an 
Echinus , the Shell being broken off ; it is one Half or Side Cryftal, 
the other Side Chalk. 
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