N A U T ILU S .
I f the animal is naturally situated in the shell, as it is figured in M r. Owen’s anatomy, it offers a
great peculiarity in its position with regard to the shell, for in most molluscous animals the shell is applied
to the back, and the apex is directed from the front, so that the last whorl b ut one o f the shell is applied to
the ventral side, where tlie gills are placed in this genus. This is the case with the cnttle fish, where, if the
apex of the bone were elongated, and twisted into a spire, the whorls would be placed as in most of the
genera o f spiral shells ; b ut in N a u tilu s , according to the figure above referred to, it is exactly the reverse of
this position, the spires being directed from the ventral side, so tha t the last whorl b ut one is applied against
the back.
A position of the shell similar to tha t here given to the Nautilus is certainly lo be found in the genera
P ate lla aw à L o ttia , where the apex of the shell is directed towards the head, instead of, as in all the other
conical shells, in which it is directed towards the tail, so tha t, if any o f these shells were spiral, the whorls
would be as in N a u tilu s ; and a somewhat similar position is also to be found in most bivalves, but it is not
easy to compare the animals of these latter shells with the Céphalopodes or Gastéropodes.
I t is certainly desirable tha t the truth o f this position should be verified. I f the animal were placed in
the shell in the opposite direction, the flap ( t. I . / . 6 . o f the illustrations of Mr. Owen’s memoir) would
explain the reason why the front p a rt o f the outer whorl is not coloured like the rest o f the shell, as this
p a rt o f the shell would then be covered from the atmosphere.
GASTEROPODES.
STROMBUS.
The foot is more or less rounded beneath, so that it can b e o f very little use for the animal to w alk upon.
There is a groove in the females on the right side of the body, which is continued across .the front edge of the
foot; the crystalline lens* o f the eyes is large, perfectly globular, and horn-coloured, and easily extracted,
by pressing the end of the pedicle o f the eye, The operculum is free for the greater pa rt o f its length, clawshaped,
and only marked with a small scar.
A young specimen of Strombus gigas, in the collection of Mrs. Atkins, which has been cut through the
cavity of the up p e r whorls, is nearly filled with a calcareous deposit of a rosy tint, and this same deposit fills
up the h inder angle of the cavities of the lower wliorls.
A PO R R H A IS .
The tentacles are far ap a rt a t the base, very long, slen d e r; the eyes are rather large, and placed near
the outer base of the tentacles ; the tru n k is large and expanded ; the foot is flat, ra the r narrow, b u t like the
foot o f other Gasteropodous M ollusca in shape ; the operculum horny, annular, small with a sub-central scar,
surrounded by a callous edge.
I t is remarkable tha t the animal o f this genus, the shell o f w hich is so like Strombus'ia character, should
be so different from tha t o f the latter. I t is figured by Muller in the Zool. Dan. t. 87.
I bave adopted the above genus, which was formed for this shell by Dacosta, as I believe it to be different
from liostc llaria— m y friend. D r. Ruppell, having informed me in a letter, that the true Rostc llaria has
an animal exactly like Strombus in form and in the position of the eyes.
• It is remavkabk tliat any person should have doubted the use of the black dot called eyes in Mollusca, as
Swaimnei'dam long ago described the humours aud crystalline lens iu the eyes of the snails [He lix ), and the iris
round the eyes of the periwinkle ( l.Utorina). The lens is to be found of a large size in most of the marlue spiral
shells, and the iris is of a different coJour in the different species of Strombs.
r 2
[ i 'H
"f- i i ' i i
. i l l
' - li