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LETTER V. 



HAMIFIED TUB1PORE....SILICIFIED TUBIPORE IN LIME-STONE.... 



MARBLE FORMED BY THIS TUBIPORE CHAIN CORAL STEL- 



LATED TUBIPORE, &C. 



1 HE specimen delineated, Plate III. Fig. 1, and which, I am in- 

 formed, was found in the neighbourhood of Mendip, in Somersetshire, 

 differs from the fossil specimens already figured, and from the recent 

 tubipore, in having neither horizontal plates, nor horizontal pipes, to 

 secure the necessary communication between the different parts of 

 the animal, disposed in the several tubes of which the tubipore is 

 composed. This office appears to have been accomplished in the 

 species of tubipore to which this specimen belonged, by the simple 

 mode of small ramifications, passing from one branch to another; not, 

 as in the species already described, in a horizontal, but in an oblique 

 direction. As far as can be ascertained by this specimen, the ramifi- 

 cations appear to have been dichotomous. This species, which it 

 seems might be properly termed tubipora ramulosa, may be described 

 as composed of tubes connected by dichotomous ramifications. 



A very curious circumstance is observable with respect to the 

 particular specimen which is here figured. It has been already re- 

 marked, that the fossil specimens, already mentioned, are sometimes 

 formed almost entirely of flint; and the necessary examination shewed 

 that, in the present fossil, every part of it which had been coral, as 

 well that part which was imbedded in the stone, as that which pro- 

 jected from its surface, was in a high degree silicious ; whilst the 

 stone which contained it was pure lime-stone. In consequence of this, 

 the stone being briskly rubbed on a silicious sand-stone, those parts 



