3ELEMNITE8. 281 



an internal coiled shell. The shells of Spirula Peronii La- 

 marck are rarely thrown ashore on Nan tucket ; it lives upon 



Pig. 222. Pearly Nautilus, N. pompilius. Seen in section showing 

 the chambers and siphuncle. Half natural size. From Tenney's Zo- 

 ology. 



the high seas. The extinct Belemnites was provided with an 

 air-cavity (phragmocone) with a straight shell, the " thunder- 



Pig. 223. Poulpe or Common Octopus of Brazilian Coast. 



bolt" fossil. Allied to Loligo and OmmastrepTies, are gigan- 

 tic cuttle-fishes which live in mid-ocean, but whose remains 



