138 



thccentral part being filled by the same kind of substance disposed 

 somewhat in a r etiform manner, projecting a little beyond the la- 

 inellated exterior part. This peculiar structure presents to the eye a 

 floscular appearance, very difficult to describe, but which is very 

 faithfully represented by the magnified figure, Plate XII. Fig. 6, a. 



By the aid of the lens it is also discovered, that the greater part of 

 the ground on which these bodies are disposed, is adorned by slightly 

 undulating, faint, and minute striir, which, in some places, appear to 

 unite with, or even proceed from, the plates of which those bodies arc- 

 formed. So numerous are these waving stria?, and so many are the 

 slight traces of them, as to render it quite fair to suppose, that they 

 were originally disposed over the whole surface. Mr. Walch describes 

 this fossil as a tubercular astroites, on a ground marked with deli- 

 cate striae ; the projecting parts, he thinks, may have been casts of a 

 columnar astroites, and now reduced to a mamillary form*. 



In Faujas St. Fond's elegant work on the natural history of the 

 Mountain of St. Peter, in which many of the riches of that immense 

 mine of fossils are displayed, two specimens are depicted, which bear 

 considerable resemblance to the fossil which now demands our atten- 

 tion. 



The one figured by Faujas St. Fond, which, in its general appear- 

 ance, approaches the nearest to our fossil, is to be found Pianche 

 XLI. Fig. 1, a. and Fig. l,b.f This specimen differs from our fossil 

 in two respects: First, the rose-like protuberances are placed with 

 a great deal of regularity, upon lines which appear to form concen- 

 tric circles round a centre, whilst in those of the fossil figured in this 

 work they are not disposed in any regular order. Secondly, the ground 

 of the fossil described by Faujas St. Fond is very finely granulated, 

 whilst in the fossil here figured, the rose-like stars are placed on a 



* Rccueil des Momimens, &c. Tome III. p. 163. 



f Histoire Naturelle de la Montague do Saint Pierre de Mae.tricat, p. 210. 



