3 ; 
LETTER Y. 
SPINES OF ECHINI. 
.ARRANGEMENT OF FOSSIL SPINES. 
It so rarely happens, except in some particular situations, and under 
some uncommon circumstances, that the spines of the echinus con- 
mue ong adherent, even to their recent shell, that it is not at all 
surprising that instances of their being connected in fossil specimens 
are exceedingly rare. Soon after the death of the animal, unless it 
happens to have been placed under such circumstances as prevent the 
ecomposition and resolution of those membraneous and muscular 
parts on which the connection depends, the spines become disen- 
the shell. This circumstance being considered, 
TL V °/ numerous cl ^ces of injury, after the death of the 
1 \ P / eY10US . to the P eriod of its becoming a subject of the 
cimens sb T? 0 ™’ * mdeed a P pears wonderful that any fossil spe- 
oimens should exist, where the shell and the spines continue united. 
in a e . op P ortumtie s of seeing the shell and spines in connection, 
iaize state, being so exceedingly infrequent, proceeds in 
a great measure the difficulty of succeeding in the attempt to asc’er- 
Tothtlf the ™ riOTS fossil spines belong. 
To he labours of Klein, Phelsum, and Leske, I must be chieflv \n 
debted for such information as I may be able to convey to you on this 
subject. I shall however endeavour, as I proceed, to confirm their 
observations, or correct their opinions, by occasional references to such 
pecimens, in my own possession, as seem to determine the relation 
d»P between the particular species of spines and of echinal shelt 
