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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. The 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, are 

 given representations of both the forms in which this fossil appears, 

 it being considered by this celebrated philosopher as referable to the 

 Madrepora 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 ter- 

 minate 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 resem- 

 blance 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 suf- 

 ficient 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 be- 

 lieve to be actually of the same species with it, is the one which is re s 



