282 OBSERVATIONS ON THE ANIMALS 
Ammoneata indicates habits, on the whole, more stationary than 
those of the Nautilacea, let us return now to the different genera, as 
they have been already described, and see what particular results we 
may obtain from studying their change of form with a similar view. 
And first the Turrilite, which is so very fragile and easily injured a 
shell that I do not know of the existence of one perfect specimen of 
any size, and that even a tolerable specimen is extremely rare. This 
shell, however, grew sometimes to an enormous size; and if we can 
even suppose that its slender siphuncle could have contained fluid 
enough to alter the specific gravity of the animal and shell so much 
as to produce motion upwards or downwards, still, when we know 
that the slightest touch would cause a fracture, it seems improbable 
that such unnecessary danger should be incurred ; and we conclude, 
surely not without reason, that this genus, at all events, was a con- 
stant inhabitant of the bottom, and that the soft mud enveloping 
the shell would be at once a defence and a place of concealment. 
The tubercles and other mechanical means by which the shell is 
strenghtened against external pressure would, it is manifest, be very 
useful in resisting the weight of the superincumbent and surround- 
ing mud. 
With regard to the next genus—the Scaphite—it is exceedingly 
difficult to give any rational hypothesis, not only as to how, but 
even where, the animal could have lived. In most specimens that 
I have seen, the shell somewhat resembles a small Ammonite with 
the last whorl or two unwound, a small part extended nearly 
straight, and the rest bent round to meet the direction of the former 
whorls. Supposing this to be the complete shell, we can conceive 
the inhabitant living in the part unwound; and the fact of its 
bending again in a contrary direction, though curious and anoma- 
lous, is not unaccountable. But there is a far more extraordinary 
form sometimes met with ; and here we seem almost completely 
baffled. It may be thus described: after the bend already spoken 
of has taken place, and the mouth of the shell has been brought 
round so as to be close to the principal spiral, the exudation of shelly 
matter seems to have gone on, and gradually approximated the aper- 
ture to the part opposed to it, at the same time diminishing the area 
of the aperture, and almost closing up the last chamber. Whether 
this is an accidental occurrence, arising from a diseased state of the 
animal, or whether there was some provision of nature to allow food 
to be taken and the animal functions to continue, are questions 
hardly to be answered in the present state of our knowledge. I 
must acknowledge myself quite at fault on the subject. On the 
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