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raised triangular processes, between each two of which is placed a 
pentagonal plate, about a quarter of an inch in thickness. 
The small one, represented Plate XVII. Fig. 5, exactly agrees, in 
every respect, with a fossil which is in the British Museum, in the same 
box with the one already described in the words of Mr. Lister and 
of Mr. Beaumont. Like that fossil, this smaller one has its trochital 
articulating surface, its five arms, and its surface made up of polygonal 
plates ; but it has no opening on the upper surface. On this part, 
instead of the opening which is observable in Mr. BeaumonFs fossil, 
there are six round protuberances of different sizes ; one projecting 
about an eighth, and the other about the thirty-second of an inch. 
The articulating surface in this fossil is very indistinctly seen : it 
appears to be formed of three pieces, the form of which cannot 
be positively ascertained. Around these are disposed six hexagonal 
pieces ; on which other smaller ones are placed, forming the visceral 
cavity; but the form and arrangement of these cannot be well made 
out. 
The fossil fragment, Plate XVII. Fig. 1, is particularly interesting 
on several accounts. The crenated articulating surface is very dis- 
tinctly observable on it, especially towards the edge of the circle. It 
is also distinctly perceived that this articulating surface is formed by 
the union of the flat surfaces of three hexagonal ossiculse, the com- 
missures of which are not, however, discoverable on the articulating 
surface, in consequence, as it appears to me, of a portion of the 
intervening cartilage still remaining adherent on the articulating 
surface. 
The ossiculse in this fossil, having a more rounded external surface, 
appear more separated than those in the preceding specimens, and 
are therefore more distinctly seen : their edges, when viewed with the 
assistance of a lens, display an osseous structure, very much resem- 
bling that which is seen on the edges of the fossil bony palates of 
fishes. 
