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species. In this specimen, the horizontal plates are much thicker 
than in the former species, and are formed of perpendicular fibres, 
which give to the section the appearance of finely-cut cork. The 
chambers, formed at the folded ends of each plate, do not appear to 
have their communication with the spaces between the plates interrup- 
ted by septa, as is in the case in Fig. 15, of the preceding species. 
In this species there does not therefore appear to be any circum- 
stance to forbid the opinion, that air, or any other fluid, being in- 
troduced into any one of the cavities, that which was next to the 
animal, for instance, might be diffused through the whole ; and, 
assuming this to be the case, we may suppose that the animal had 
the power of occasionally changing its degree of buoyancy, by an 
appropriate change in the contents of these cavities. 
After destroying numerous specimens, for the purpose of ascer- 
taining the real structure of this fossil, I succeeded in breaking the 
specimen from Verona, Plate X. Fig. Vj ? m such a manner as 
brought a part of its internal spiral wreath into view. The appear- 
ance of this gave strong reason for believing, that the communication 
between the cavities was without any interruption, no septa being dis- 
coverable by a lens, nor even with the aid of a double microscope. In 
this specimen the plates had evidently been connected by short colum- 
nar bodies, the points of adherence of which are plainly discoverable. 
Assuming an unity of principle in the economy of these animals, 
and seeing in these specimens no reason to suppose that the com- 
munication between the cavities was interrupted, may there not be 
some reason for supposing that a communication may exist in all the 
species, although too minute to be discovered ? 
The wide separation observable along the centre of the specimen, 
Plate X. Fig. 19, with other similar appearances, in a less degree, 
in other specimens, induce me to make it a question, whether the 
animal might, or not, have had the power of approximating, and 
