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LETTER V. 
RAMIPIED TUBIPORE SILICIFPED TUBIPORE IN LIME-STONE 
MA'RBLE FORMED BY THIS TUBIPORE CHAIN CORAL STEL- 
LATED TUBIPORE, &C. ' 
The specimen delineated, Plate III. Fig. 1, land 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 jparts of 
the animal, disposed in the several tubes of which ,the tubipore (is 
composed. This office appears to ffiave been accomplished in ithe 
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 tubipore ramulosa, may be described 
as composed of tubes connected by dichotomous ramifications. 
A very curious circumstance is observable with respect to tthe 
particular specimen which is here figured. It has been remarked, 
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 
