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colours have only the internal nacre of the shell adherent ; and not as 
in this, and in one other calcareous specimen, which I possess, the 
whole substance. In some small specimens with which I have been 
favoured by the Rev. J. R. Cleeve and Mr. Clarke, the cavities are 
filled by a transparent calcedony ; whilst the external opaque silicious 
substance yields every appearance to warrant the supposition of its 
being the shell itself, thus changed by impregnation with silex ; for, 
although the change is such, as to have given transparency to the 
mass, the smooth shelly surface is evident. 
Plate X. Fig. 6 and *], are the lateral and front views of a beautiful 
fossil, which the late Mr. Martin, in his admirable work, Pertrijicata 
Derbiensia, PI. 40, Fig. 1, 2, gives, rather hesitatingly, as anautilites, 
with this description — “ A fossil shell. The original a Nautilus. 
Involuted, somewhat globose, imperforated, striated ; the striae close, 
acute, transverse, but oblique on the sides, and united by a single, 
narrow, dorsal line, at the ambit. The mouth or aperture large, and 
somewhat extended on each side. The form and situation of the dis- 
sepiments unknown. Now and then found in our lime-stone, but not 
frequent.” I have rubbed down this fossil at the mouth, but without 
being able to ascertain any thing with respect to either septa or si- 
phunculus ; and, of course, without being able to determine its genus. 
Plate X. Fig. 8, is a fossil shell of a very rare form. It is rather 
globose, and marked with numerous transverse furcated lines, and 
three deep grooves, which surround the whirl, and terminate on each 
side in a small, but deep umbilicus. It possesses the character of Am- 
monites, m. having small and frequent foliaceous sutures, with, of course, 
sinuous septa, and the character of Nautilus, in the outer turns, in- 
volving the inner. With the habitat of this shell I am unacquainted. 
In another fossil from Italy, six times the size of the preceding, 
and much flatter, an exact agreement with the preceding exists, 
except that it is flatter. 
Plate X. Fig. 9, is a fossil, which is also of an ambiguous appear- 
