430 PHILOSOPHY OF ZOOLOGY. 



The two Linnaean genera, Nautilus and Sepia, compre- 

 hend all the animals which are at present considered as be- 

 longing to this class. 



Order I. Nautilacea. 



Furnished with a multilocular shell. 



This order is involved in the greatest obscurity. None 

 of the recent species have been subjected to an accurate 

 examination, so that their connection with the order Sepia- 

 cea may still be considered doubtful. Enough is known 

 of the animals of two of the genera, to furnish some 

 hints for those who are fond of classifying animals from 

 their analogies. These genera are Spirula and Nau- 

 tilus. 



In the Spirula, the shell, which is concealed under the 

 skin of the back, is spiral, with the whorls separate, the 

 mouth orbicular, the chambers perforated by a pipe, and 

 the last cell produced into a tube. The position and use 

 of this terminal tube are unknown. The S. vulgaris is 

 the most common species, and inhabits the seas in the West 

 Indies. In the restricted genus Nautilus, the shell is sup- 

 posed to be external, and the body of the animal to be 

 lodged in the last chamber, and to be fixed by a ligament 

 which descends into the central pipe. In the shell itself, 

 the turns of the spire are contiguous, and the last whorl 

 embraces the others on the sides. The N. pompilus of 

 RuMPHius is the only species in which the animal has been 

 detected. 



The other genera which have been formed in this order 

 depend exclusively on the characters furnished by the 

 shells ; and the resemblance which these bear to the pre- 



