[ * 5 '^ 3 
into flint ; or, in other words, that flint was produced 
by chalk originally. And indeed I have many fpeci- 
mens myfelf, that feem to prove it; in fome of which 
they feem to fhew the gradual change from the one 
to the other, not at all like a fudden appofltion of 
chalk to flint. 
Other kinds of echinites, fuch as the Echini cor- 
dati^ or heart -fhaped echinite, the pileati or conic, 
the galeati or helmet-fliaped, with feveral other 
kinds, are often formed of other fpecies of flony 
particles. 
The foflil before you, being one of the oval kind, 
with large papillae, is the Echinometra digitata Je- 
cunda rotunda vel cidaris Mauri of Rumphius^ which, 
with the other oval echinites, are very rarely found 
but in chalk : and it is remarkable, that whether they 
are filled with chalk, flint, or chryftal, their fiiells 
break with a felenitical appearance, juft as the lapides 
Judaici, and all other fpecies of echinites found in 
chalk-pits, do. 
XXVII. 
