136 UNIVALVES. 



Genus. NAUTILUS.* Plural, Nautili. 



SAILOR. 



Generic Character. Shell univalve, spirally 

 convoluted, smooth, multilocular ; f chambers 

 perforated and connected by a siphunculus or 

 pipe ; the dissepiments are convex inwardly, the 

 chambers gradually increase in size from the 

 apex. The animal resides in the last. 



OBSERVATIONS ON THE SHELL AND ITS 

 INHABITANT. 



The Nautili differ much in size ; some being 

 too minute to be observed by the naked eye, 

 while others are a foot in diameter. In some the 

 whorls are contiguous ; in others they are de- 

 tached. The tube which connects the chambers 

 is supposed to admit either air or water as the 

 animal requires ; when the shell is stationed at 

 the bottom of the sea the siphon is filled with 

 aqueous fluids ; by excluding these the gravity of 

 the shell is diminished, and it rises in 'conse- 

 quence to the surface ; when on the contrary the 

 animal is inclined to descend, it contracts itself 



i 



* Plate VI. figure 4. 



f Multilocular, having many little chambers, from the 

 Latin words, multus, many, and loculum, a little chamber. 



