103 



another contrivance is adopted, apparently for the production of this 

 effect the rendering the weight of the mass so near to that of water, 

 that a very slight change may occasion or destroy its buoyancy. 



Should the opinions here offered be found to be objectionable, it may 

 be considered, in excuse, that the economy of the animal has hitherto 

 undergone but little investigation. So little, indeed, has the structure 

 and the nature of the siphunculus been understood, that even De Bosc, 

 the latest writer, perhaps, on the subject, points out no other use of 

 this tube to the animal, that of its serving to conduct its tail to the 

 beginning of the spire. " II n'y a pas de doute que ce tuyau ne serve 

 a conduire la queue de Panimal a Porigine de la spire ou elle s'attache." 

 Histoire naturelle des coquillcs, Tome V. p. 1 64. 



We at present know, in a recent state, and of a size sufficiently large 

 to allow of an examination of the structure, without the aid of a micro- 

 scope, but one species of nautilus, N. pompilius. There is, however, no 

 doubt of several distinct species existing in a mineralized state. 



In Shepey Island, in the corresponding stratum of Brentford, in 

 some parts of Somersetshire, particularly near Bath, and, I doubt 

 not, but in several other parts of this island, a fossil nautilus is found, 

 which, from the roundness of the back part of the shell, may be con- 

 cluded to approach exceedingly near, at least in its form, to N. pompilius. 

 Some of these, which have been found at Shepey, where they are 

 mostly imbedded in septaria, as well as those which have been found at 

 Brentford, are of very considerable magnitude, and seem to resemble 

 N. pompilius in their internal structure. 



The outside of these fossils are frequently resplendent, with a 1 pearly 

 coat. This circumstance demands some little consideration ; since, as 

 this is not the case with the outside of the shell of N. pompilius, it seems 

 to point out the fossil as a different species, as the nacre does not exist 

 on the outside of the shell of the recent species. Future observations 

 will determine this question more decidedly; but at present, I am dis- 

 posed to imagine, that, in the fossil specimens, the external part of 



