134 UNIVALVES. 



GENUS. NAUTILUS.* 



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 tlie 

 apex. The animal resides in the latter. 



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 within its boat, draws in water, and imme- 

 diately disappears. Though capable of floating 



* Plate VI. figure 4. 



f Multilocular, having many little chambers, from the Latin 

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



