140 



several specimens of fossil mother-of-pearl from the Nautilus; but, where the 

 colours are not entirely lost, the appearance is exactly similar to that of 

 the recent substance. 



Specimens of the Cornu ammonis, on which the brilliant nacre still 

 exists, are sometimes found. At Broad Marston, as we are informed by 

 Dr. Maton *, a stratum was found, in 1778, containing a congeries of 

 Cornua ammonis, on which the nacre is still visible : and indeed, on some 

 of these, the brilliancy of colour possessed by the nacre is very consider- 

 able. The finest British specimens of this kind, which I have seen, are 

 in the valuable collection of Mr. Harcourt, of Stapleton. 



But the specimens which display the naost vivid colouring, are those 

 which are found near the river Moscorcica, about a league from Moscow. 

 In one of these specimens, which I obtained from Mr. Heuland, the colours 

 are not less splendid, nor less beautifully changeable, than those which the 

 fire-marble itself displays, and are finely disposed over the whole of the 

 shell. In another specimen, either from France or from the neighbour- 

 hood of Moscow, the colour is the richest blue I have ever seen. 



Such of these shells as are found in schistose strata have generally 

 suffered from compression; as is mostly the case, indeed, with all 

 organic remains which have been thus preserved. This is particularly 

 the case with the ammonites which are found at Watchett. In these spe- 

 cimens, it often happens that the whole substance of a large shell is com- 

 pressed into the thickness of a quarter of an inch. In ammonites which 

 have been thus preserved, the shell is sometimes of a dead opaque 

 white, whilst in others it reflects the most beautifully-coloured rays. 



The specimen represented Plate IX. Fig. 8, and which is, I believe, 

 foreign, is very interesting, not only from its figure, but from its retain- 

 ing a considerable portion of the original shell. Specimens of this kind 

 are extremely rare ; for, in general, those which exhibit brilliant co- 

 lours have only the internal nacre of the shell adherent; and not as 



* Dr. Maton's Tour to the Western Counties of England, Vol. I. p. 21. 



