GASTEROPODA. 5 
shells are, and of how little value the marks usually depended upon 
as specific really are. ‘The following are among some of the conclu- 
sions deduced. 
1. That the general and the ornamental colours of the same species 
may vary indefinitely. The markings will sometimes be in flam- 
mules, in coarse or fine zigzag lines, in triangular blotches, &c. 
2. The presence of a tongue (languette) to the columella is acci- 
dental and not of specific value, as among a number of specimens un- 
equivocally of the same species, some will possess it and others not. 
It is probably the result of advanced age. 
3. The colouring about the septum, especially the presence of dark 
blotches, is accidental, and occurs in all species. 
4. The width or area of the muscular impression varies very much 
in shells which, beyond all question, are the same, and therefore cannot 
be taken as a specific character. 
One of the species obtained is doubtless N. Suffreni, Recluz; and 
exhibits wide variations in size. Some of them have a gummy exte- 
rior, which causes them to seem granulated or wrinkled. The most 
important character of the species is, the very obliquely shelving posi- 
tion of the septum, and, generally, its very broad, muscular impres- 
sion. 
Another equally common species, which I should not hesitate to call 
N. Freycineti, Recluz, were it not that it is said to be a Macassar shell, 
has a very simple and uniform colouring, with a very narrow, nearly 
horizontal septum, of a pale yellow colour; the muscular impression 
is, generally, quite narrow. 
A third species, from Tahiti, may be different still. It is more 
tectiform, especially near the spire, dark coloured and shining. It 
may be N. Entrecasteauz, Recluz. 
Navice.La Freycineti (?), (Reciuz), Rev. Zool., 1842, p. 120. 
The antmat of the shell supposed to be the above species is small, 
ochreous above, with short, olivaceous, interrupted lines; beneath 
