37 



LETTER V. 



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 continue 

 long 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 decomposition and 

 resolution of those membraneous and muscular parts on which the con- 

 nection depends, the spines become disengaged, and fall off from the 

 shell. This circumstance, being considered, with that of the numerous 

 chances of injury, after the death of the animal, and previous to the 

 period of its becoming a subject of the mineral kingdom, it indeed ap- 

 pears wonderful that any fossil specimens should exist, where the shell 

 and the spines continue united. 



From the opportunities of seeing the shell and spines in connection, in 

 a mineralized state, being so exceedingly infrequent, proceeds, in a 

 great measure, the difficulty of succeeding in the attempt to ascertain the 

 particular species to which the various fossil spines belong. To the 

 labours of Klein, Phelsum, and Leske, I must be chiefly indebted for 

 such information as I may be able to convey to you on this sub- 

 ject. I shall however endeavour, as I proceed, to confirm their observa- 

 tions, or correct their opinions, by occasional references to such speci- 



