64 
EXPLANATION Ol' PLATE 32. 
a double keel-shaped indented process, enlarging 
from its apex backwards.* (Original.) 
Plate 32. V. I. p. 323. 
Fig. 1. Part of the petrified shell, and casts of the 
interior of some of the chambers, of a Nautilus 
hexagonus, from Marcham, Berks. This fossil ex- 
hibits at its smaller End, from d. to h,, a series of 
casts of the Air chambers, from which the external 
shell has been removed. The cavity of each cham- 
ber is filled with a disc of pure calcareous spar, 
representing the exact form of the chamber into 
which it had been infiltrated. In the larger portion 
of this fossil, the petrified shell retains its natural 
place, and exhibits fine wavy lines of growth form- 
ing minute llibs across its surface. (Original.) 
Fig. 2. Fractured shell of N. hexagonus, from the Cal- 
careous grit of Marcham. The chambers are lined 
with calcareous spar, and a circular plate of 
the same spar is crystallized around the siphon. 
The intei’ior of the siphon is filled with a cast of 
Calcareous grit, similar to that which forms the 
rock from which the shell was taken. See V. I. 
p. 326. f (Original.) 
* Although the resomblauces between these fossil beaks, and that 
of the animal inhabiting the N. Pompilins, are such ns to leave no 
doubt that Rhyncholites are derived from some kind or other of 
Cephalopod, yet, as they are found insulated in strata of Muschel 
kalk and Lias, wherein there occur also the remains of Sepiae that 
had no external shells, wc have not yet sufficient evidence to enable 
us to distinguish between the Itliyncholites derived from naked Sepiae, 
and those from Cephalopoda that were connected with chambered 
shells. I possess a specimen of a fossil Nautilus from the Lias at 
Lyme Kegis, in which the external open chamber contains a Ehyu- 
cholite. 
1 This fossil exhibits the Siphuucle in its proper place, passing 
