22 



of this part from its earliest and youngest form, when it possessed a width and 

 elevation not exceeding one-fourth of a line, to its mature growth, and the size of 

 some inches. The very minute bases above mentioned/ adhere to a superior 

 columnar joint (T. ii. fig. l.)and possess in the centre a very minute column sur- 

 rounded by laminae which form a small regular cone. These, in combination 

 with numerous other specimens in different stages of growth, and with their lon- 

 gitudinal sections, prove that the exuded calcareous matter forming the pedicle 

 or base, became completely indurated soon after its deposition, since the 

 lowest columnar joints to be traced at the bottom of the base are very minute, 

 (PL. n. fig. 3. and 4.) not exceeding the proportions of the youngest specimens, 

 (and must therefore have been prevented from increasing and expanding in their 

 growth by the unyielding nature of materials surrounding them) whilst the 

 succeeding joints become in series at certain intervals of four, five, or even 

 more, successively larger and larger. It may also be seen that the inferior 

 portions of the alimentary canal enveloped in the base, become gradually filled 

 up and obliterated, being no longer required in this part of the animal (T. IL 

 fig. 4. and 10.) where all increase had long ceased* 



The secretions of the indurating calcareous matter took place in consider- 

 able quantity when the animal grew up, and appears to have flowed abundantly 

 from vessels between the radiating surface of two joints. This is beautifully dis- 

 played in sections of large bases (T. n. fig. 10.) where the differently coloured 

 laminae demonstrate the gradual formation of this part, their lines and the man- 

 ner in which they spread over and encompass extraneous matter which happened 

 to be in their way, proving the original fluidity, or rather viscidity of the mass. 



These lines prove also decidedly that the irregular conical mass of the base 

 is made up of distinct laminae, concentric and parallel to the outer surface of the 

 cone, placed one within the other, and resulting from successive or periodical 

 increase by deposition. In longitudinal sections, as we have already stated, 

 these lines are decidedly seen, but lines of separation are also seen traversing 



* These very minute bases are interesting, as affording a proof that the propagation of these 

 animals must have been oviparous; since from their size they must hare belonged to the very 

 earliest and almost embryotic state of the animal ; and yet are found affixed, not to the parent's body, 

 but to a dead plate ; whereas the offspring produced by gemmiferous generation, nerer becomes de- 

 tached from the parent'j body till it has obtained a considerable iie. 



