56 
EXPLANATION OF PLATES 33. 34. 
Plate 33. V. I. pp. 326, 327. Note. 
Longitudinal Section of Nautilus Striatus, from the Lias 
at Whitby, in the collection of Mrs. Murchison, The in- 
terior of the Chambers is filled exclusively with calcareous 
spar, and that of the Siphuncle with Lias. (Original.) 
a. The Siphuncle: the union of the siphuncular calca- 
reous sheaths, with the aperture or collar of each 
transverse Plate, is so closely fitted, that no fluid 
could have passed between them into the air cham- 
bers. 
b. One of the transverse Plates forming the Air cham- 
bers. 
c. White calcareous spar, filling the middle region only 
of the air chambers. 
d. Stratified zones of dark coloured calcareous spar, de- 
posited in equal thickness on both sides of the 
transverse plates, and also on the inside of the shell, 
and around the calcareous sheath of the siphuncle.* 
e. Portion of the external shell, shewing a laminated 
structure. 
Plate 34. V. I. p. 329. Note. 
Drawing of the animal of tlie Nautilus Pompilius, pre- 
pared at my request by Mr. Owen, to shew the manner 
in which the siphuncle terminates in the Pericardium. 
(Original.) 
* The successive zones of tliis dark Spar shew that the Lime com- 
posing it was introduced by slow and gradual infiltrations into the 
cavity of the air chambers. Hence it follows that no communication 
existed between the Siphuncle and these chambers, at the time when 
this Pipe was filled with tlie fluid mud, that has formed a cast of Lias 
within it. As the fractures across the Siphuncle in the 2nd and 3rd 
chambers are filled only with spar, of the same kind as that within 
these Chambers, these fractures could not have existed, when the 
Mud of the Lias formation entered the Siphuncle, without admitting 
it also into the chambers adjacent to them. 
