MOLLUSCOUS ANIMALS. 
107 
CEPHALOPODES. 
NAUTILUS. 
If the animal is naturally situated in the shell, as it is figured in Mr. 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 but one of the shell is applied to 
the ventral side, where the gills pre placed in this genus. This is the case with the cuttle 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 of spiral shells ; but in Nautilus, according to the figure above referred to, it is exactly the reverse of 
this position, the spires being directed from the ventral side, so that the last whorl but one is applied against 
the back. 
A position of the shell similar to that here given to tire Nautilus is certainly to be found in the genera 
Patella and Lottia, 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 that, if any of these shells were spiral, the whorls 
would be as in Nautilus ; 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 Cephalopodes or Gasteropodes. 
It is certainly desirable that the truth of this position should be verified. If the animal were placed in 
the shell in the opposite direction, the flap ( t . 1 . f. 6. of the illustrations of Mr. Owen’s memoir) would 
explain the reason why the front part of the outer whorl is not coloured like the rest of the shell, as this 
part of the shell would then be covered from the atmosphere. 
GASTEROPODES. 
STROM BUS. 
The foot is more or less rounded beneath, so that it can be of very little use for the animal to walk 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* of the eyes is large, perfectly globular, and horn-coloured, and easily extracted, 
by pressing the end of the pedicle of the eye. The operculum is free for the greater part of its length, claw- 
shaped, 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 upper whorls, is nearly filled with a calcareous deposit of a rosy tint, and this same deposit fills 
up the hinder angle of the cavities of the lower whorls. 
APORRHAIS. 
The tentacles are far apart at the base, very long, slender ; the eyes are rather large, and placed near 
the outer base of the tentacles ; the trunk is large and expanded ; the foot is flat, rather narrow, but like the 
foot of other Gasteropodous Mollusca in shape ; the operculum horny, annular, small with a sub-central scar, 
surrounded by a callous edge. 
It is remarkable that the animal of this genus, the shell of which is so like Strombus in character, should 
be so different from that of the latter. It is figured by Muller in the Zool. Pan. t. 87. 
I have adopted the above genus, which was formed for this shell by Dacosta, as I believe it to be diffe- 
rent from Post Maria — my friend, Dr. Ruppell, having informed me in a letter, that the true Rostellaria has 
an animal exactly like Strombus in form and in the position of the eyes. 
* It is remarkable that any person should have doubted the use of the black dot called eyes in Mollusca, as 
Swammerdam long ago described the humours and crystalline lens in the eyes of the snails {Helix), and the iris 
round the eyes of the periwinkle { Liltorina ). The lens is to be found of a large size in most of the marine spiral 
shells, and the iris is of a different colour in the different species of Strombs. 
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