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careous matter, of which the preceding fossils of this district have 
been found to consist. Two distinct forms are in general to be found 
on the masses which owe their figures to this zoophyte. 1 he one of 
these is nearly a hemispherical concavity ; a slightly rising, oblong 
prominence possessing its lower part. The sides of this cavity are 
formed of knotted or articulated tubes or fibres, which pass, side by 
side, from its circumference, and terminate at the bottom, in a line, 
on the oblong prominence, Fig. d. The other is a nearly flat, circular 
space, covered with concentric risings and depressions, and radiating 
striae. Fig. 11, e. 
In the work of Faujas St. Fond, Plate XXXVII. Fig. 8, 9? given 
representations of both the forms in which this fossil appears, it being 
considered by this celebrated philosopher as referable to the Mad'i epot u 
Porpita, Linn, already examined in the commencement of this volume. 
It is not without due consideration that I venture to differ from such 
respectable authority, but comparison immediately manifests essential 
differences between the two fossils : omitting to notice others, it may 
be sufficient to remark that, in the madrepora porpita, the radiating 
fibres originate from a point in the centre of the madrepore ; but in the 
fossil now under examination, they terminate in a line which is nearly 
three-fourths of its length. 
I should not, however, have been disposed, I must acknowledge, to 
separate this fossil from the porpital madreporite so decidedly, had I not 
also seen reason to believe that it bore a tolerably close resemblance 
to a zoophyte, which we have already noticed. Indeed it may be 
adduced as one of the numerous instances in which, for want of a 
sufficient illustrative specimen, conjectures are formed, possessing almost 
every appearance of probability, but which, on the discovery of such 
a specimen, are found to be unfounded and absurd. The fossil with 
which I conceive this bears so close a resemblance, and which I believe 
to be actually of the same species with it, is the one which is re- 
