56 
of colour and indifferent polish, it is not a very beautiful stone. It is 
found in the island of Sardinia, as also in some parts of Switzerland.* 
Madrepora undulata is formed of large elevated stars, with elongated 
bending rays. Like the former, this is found only in a mineralized 
state. Specimens of the same species in calcareous stone are fre- 
quently found in Sweden, Switzerland, and in England. The exa- 
mination, with a lens, of a specimen of this kind from the neighbour- 
hood of Bristol, manifests a considerable degree of similarity of struc- 
ture between this coral and that of the madrepora vermicularis^ the dif- 
ference appearing chiefly to consist in the magnitude of the m. undulata 
exceeding that of m. vermicularis. In the specimen referred to, which 
is a soft calcareous stone, a few of the conical summits of the stars are 
broken, by which a transverse fracture of the coral is obtained, dis- 
playing a similar figure, on a smaller scale, with those displayed in the 
marble. Fig. 10. 
Mons. Bertrand, speaking of those stones which had their surface 
marked with risings of stellated figures in relief, says, these stones are 
not as Scheuchzer, Volkmann, and all the authors who have spoken 
of them, have believed, corals themselves, but rather moulds or im- 
pressions of stellated corals made whilst the strata of which these stones 
are formed, were in a soft state.-f* But the fossil here figured places 
their existence beyond a doubt ; since the projecting star is evidently the 
body of the coral, converted into a spathose substance. 
The specimen figured Plate VI. Fig 12 and 13, bears a consider- 
able resemblance, in the formation of its stars, with that of Plate VI. 
Fig. 10, but differs from it very considerably in other respects. The 
substance of the fossil which is here figured is a light reddish grey horn 
stone ; but the colour varies a little in different specimens. In some it 
* The Natural History of Fossils, by Emanuel Mendes Da Costa. P. 249. 
t Dictionnaire Universel des Fossiles, par M. E. Bertrand. 1763. 
I 
