COMPARED WITH THAT OF NAUTILUS POMPILIUS. 
283 
comiriencing anteriorly with an azygos transverse lamina. In both kinds, however, 
I have distinctly traced out the corresponding tentacula, with such minor differences 
as might be expected to occur in different specimens of either separately. The ques- 
tion here naturally arises, — Are the peculiarities observable in the descriptive and 
microscopic anatomy of each of sufficient importance to entitle them to be considered 
distinct species, or are they within the pale of that latitude which must be allowed 
to variety ? 
Any tendency in a being to revert to an original type, when such has been deter- 
mined, betrays variety ; but this tendency in the Nautili now under consideration is 
never manifested by the occasional occurrence of specimens presenting characters 
which place them intermediate between N. Pompilius and N. umhilicatus. 
Having visited the Fijii Islands since my former paper on the N. Pompilius was 
written, I find that the umbilicated Nautili are not known to the natives, although 
N. Pompilius is very plentiful ; but at Fatuna or Wallis’s Island, where both are found, 
the people recognize the difference between them, depending upon the presence or 
absence of umbilical pits. Now, although particular localities, with all attending 
circumstances, may favour the production of varieties, yet the permanence of the 
distinctive characters of these Nautili without symptom of amalgamation, and the 
discovery of a female specimen of N. umhilicatus, strongly support the view that 
they are distinct species, though very closely allied. 
Explanation op the Plates. 
PLATE XIV. 
Fig. 1. Left lateral view of N. umhilicatus removed from the shell. 
a. Eye. 
h. Hood. 
c. Tentacular sheaths. 
d. Digital tentacula. 
ee. Ocular tentacula. 
f. Subocular hollow process. 
g. Funnel lobe. 
h. Mantle. 
i. A lobe of the mantle which rests upon the black-stained patch of 
the shell. 
j. A process similar to the last, beneath which it lies in the hollow 
of the hood, being continuous with the portion or part of the 
funnel lobe. 
1i. Shell-muscle. 
2 Q 
MDCCCLV. 
