173 
and filled by the drusy crystallization of tufa. The animal part suffers 
decomposition, in the manner just described, by the constant action of 
simple water, whilst the crystalline calcareous matter, suffering little or no 
change, retains perfectly the forms which it had derived from the animal 
remains which have passed away. 
In this manner, I presume, the calcareous casts of shells, &c. have 
been preserved in the Mountain of St. Peter ; and thus also I suppose 
the parts of the vertebral column have been removed in the specimen 
which gave rise to these remarks, whilst the perfect form of the cavity 
of the column has been preserved. Calcareous casts of these bodies 
are, however, I believe, very scarce, when compared with those which 
are formed in Chert. 
LETTER XVII. 
LILY ENCRINITE TRUNK PELVIS SUPERIOR EXTREMITIES 
NUMBER OF BONES IN THE SUPERIOR PART OF THE ANIMAL.... 
INFERIOR EXTREMITY. 
F ROM the view which has been hitherto taken of the component parts 
of the vertebral columns of fossil encrini, no doubt can exist of their being 
divisible into several species : to discover the respective characters of these 
species is now to be attempted. 
From this same general view of the mineralized remains of these 
animals, there appears to be sufficient reason for adopting the follow- 
ing definition, as containing the generic characters of the fossil en- 
crinus ; 
Encrinite, the lapidified skeleton of a zoophyte; in which pentago- 
% 
