EXPLANATION OF PLATE 32. OO 



Fig. 3. represents in its natural size, a portion of tlie 

 Siphuncle which in Fig. 2. is laid bare along its 

 course through the chambers, d. e.f. In the trans- 

 verse Plate, hj the siphuncular collar is entire, but 

 a Section of another collar in the transverse Plate, 

 7, shews 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 chambers. As in the recent Nautilus 

 Pompilius, there is no communication between the interior of the 

 Siphon and 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- 

 phuncle, surrounded externally with calcareous spar, and filled 

 internally with Grit. Other Sections of the Siphuncle at h. d. e.f. 

 shew the calcareous Grit within its cavities to be contracted at its 

 passage through the collars of the transverse plates, and most en- 

 larged midway between one transverse plate and another. 



This fossil affords two proofs that no communication existed between 

 the interior of the Siphuncle and that of the Air chambers. 1st. 

 the calcareous sheath of the Siphuncle is seen at d. e.f. completely 

 enclosing the calcareous grit which forms the cast within it. 2dly, 

 had there been any communication between the interior of the si- 

 phuncle, and that of the air chambers, these chambers must have 

 received some portion of the materials of the grit that have filled 

 this Siphuncle : not a particle of grit is found in any one of the 

 adjacent air chambers, but they are all lined, and some of them 

 nearly filled with a crystalline deposit of Carbonate of Lime, disposed 

 in uniform plates around the interior of each chamber, and around 

 the Siphuncle. See Fuj. 2. c. c'. a. «'. a^. a^. and Fig, 3. d — h. This 

 deposit can only have been formed from water charged with carbo- 

 nate of lime, introduced by infiltration, after the interment of the 

 shell, and filling the chambers which are thus uniformly invested. 



