explanation or plate 32. 
't3' 3. lepresents in its natural size, a portion of the 
^iphuncle which in Fig. 2. is laid bare along its 
course through the chambers, d. e.J\ In the trans- 
verse Plate, h, the siphuncular collar is entire, but 
a Section of another collar in the transverse Plate, 
*, shew’s the contraction of the Siphon at its passage 
through this aperture, and exhibits also the over- 
lapping, or squamous suture by which the Collar 
is fitted to the superior and inferior portions of the 
calcareous Sheath of the Siphon. See V. I. pp. 
326, 327. Note. (Original.) 
A similar structure may be seen at the Collars 
of the transverse Plates of the N. Striatus. See 
PI. 33. 
across the cavities of the Air chamhers. As in the recent Nautilus 
Pompilius, there is no communication hetweeii the interior of the 
Siphon ami that of the Air chambers, so in this fossil shell, there is 
proof that no communication existed between these cavities. A 
transverse section at a, shews the thin edge of the sheath of the si- 
Pl'uncle, surrounded externally wdth calcareous spar, and filled 
"'■ith Grit. Other Sections of the Siphuucle at b. d. e.f. 
GW the calcareous Grit within its cavities to he contracted at its 
passage through the collars of the transverse plates, and most en- 
orged midway between one transverse plate and another. 
nis lossil affords two proofs that no communication existed betw'ecn 
le interior of the Siphuncle and that of the Air chambers. 1st. 
16 calcareous sheath of the Siphuncle is seen at d. e. f. completely 
had calcareous grit which forms the cast within it. 2dly, 
A there been any communication between the interior of the si- 
^ Uncle, and that of the air chambers, these chambers must have 
^cceived some portion of the materials of the grit that have filled 
Us Siphuncle: not a particle of grit is found in any one of the 
Jaceiit air chambers, but they are all lined, and some of them 
in ^ ®^^6d with a crystalline deposit of Carbonate of Lime, disposed 
ti plates around the interior of each chamber, and around 
U6 Siphuncle. See Fig. 2. c. c'. c. a', u^. a?, and Fig. 3. d — k. This 
^ posit can only have been formed from water charged with car- 
of lime, introduced by infiltration, after the interment of the 
® > and filling the chamhers which are thus uniformlv invested. 
