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, suf- 

 fering 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 sup- 

 pose 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. ...v 

 INFERIOR EXTREMITY. 



ROM the view winch has been hitherto taken of the component 

 parts of the vertebral column 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 mineralised 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- 



