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XII. On the Anatomy of Nautilus umbilicatus, compared with that of Nautilus 
Pompilius. By John Denis Macdonald, R.N., Assistant-Surgeon of H.M.S.V. 
‘ Torch,' commanded by Lieut. William Chimmo, R.N., tender to H.M.S. ‘ Herald^ 
Captain H. M. Denham, R.N., F.R.S., commanding the Expedition to the South 
Seas. Conmiunicated by Sir William Burnett, K.C.B. Sfc. 
Received February 22, — Read March 22, 1855. 
Her Majesty’s Steam-Vessel ‘Torch ’ having visited the Isle of Pines in the month 
of July 1854, one of the officers had the good fortune to pick up a recent specimen 
of Nautilus umbilicatus on the outer reef off Observatory Island. The creature had 
most probably been thrown up by the waves, and remained within a ledge of coral 
when the spring tide receded. The natives frequently find Nautili entrapped in this 
way, but we could not prevail upon them to bring us the recent animals, although a 
liberal remuneration was offered. 
The specimen forming the subject of the present paper was alive when brought on 
board, but it was too much exhausted to exhibit any active movements when placed 
in a vessel containing sea-water. On touching the tentacula they curled up, or 
moved about irregularly, and the muscular fibres of the funnel lobe contracted 
slowly, without however producing respiratory currents. 
A considerable portion of the posterior part of the hood appeared to have been 
eaten away by some predaceous enemy, but in other respects the animal was perfect. 
On comparing the Nautilus Pompilius with Nautilus umbilicatus in the recent state, 
besides the remarkable differences existing between their respective shells, one is 
struck with the deep position of the latter animal when fully retracted, the space 
between the upper surface of the hood and the lip of the shell being so considerable, 
that in the lateral view no part of the creature is visible. On the other hand, the 
animal of N. Pompilius completely fills the chamber of ocyjupation, and many of the 
tentacula, with a large portion of the hood, rise above the peristome of the shell, so 
that when the soft parts are removed the rounded orifice of the siph uncle may be 
distinctly seen in the last-formed septum. Not so however with N. umbilicatus ; on 
account of the great depth of the chamber in which the animal is lodged, the open- 
ing of the sipbuncle cannot be seen in the empty shell. It must be remembered, 
however, that when a new septum is formed, the last chamber is comparatively 
shallow, and it continues to deepen as new additions are made to the lip of the shell 
until the development of another septum is necessitated. 
Apart from the shells, these two species, if indeed they may be considered distinct, so 
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