154 



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 interrupted by septa, 

 as is the case in Fig. 15, of the preceding species. 



In this species there does not therefore appear to be any circumstance to 

 forbid the opinion, that air, or any other fluid, being introduced 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 ascertaining 

 the real structure of this fossil, I succeeded in breaking the specimen 

 from Verona, Plate X. Fig. 17, in such a manner as brought a part of 

 its internal spiral wreath into view. The appearance of this gave strong 

 reason for believing, that the communication between the cavities was 

 without any interruption, no septa being discoverable by a lens, nor even 

 with the aid of a double microscope. In this specimen the plates had 

 evidently been connected by short columnar bodies, the points of adhe- 

 rence of which are plainly discoverable. 



Assuming an unity of principle in the economjNof these animals, and 

 seeing in these specimens no reason to suppose that the communication 

 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 powe*r of approximating, and 



