CEPHALOPODA. 313 



forming an angle between them, thus producing an elongated cone, 

 spirally convoluted in one plane and divided transversely into cham- 

 bers. Such is the shell of the Spirula, w^hich has additional cha- 

 racters consisting of a single hollow column that occupies the inter- 

 nal side of each chamber, continuing its tube with those of the other 

 chambers to the very extremity of the shell — this column is termed 

 the siphon. The turns of the spire do not come into contact. 



But a single species, Nautilus spirula, L.j List., 550, 2, is 

 known. The 



Nautilus, properly so called, 



Has a shell which differs from the Spirula in the sudden crossing 

 of the laminae, and in the last turns of the spire, which not only 

 touch the preceding ones but envelope them. The siphon occupies 

 the centre of each septum. 



iV. pompilius, L.; List, 551, the most common species; it is 

 very large, formed internally of a beautiful nacre, and covered 

 externally with a white crust varied with fawn-coloured bands 

 or streaks. 



The animal, according to Rumph, is partly contained within 

 the last cell, has the sac, eyes, parrot-beak, and funnel of the 

 other Cephalopoda; but its mouth, instead of having their large 

 feet and arms, is surrounded by several circles of numerous 

 small tentacula without cups. A ligament arising from the 

 back traverses the whole siphon and fastens it there(l). It is 

 also probable that the epidermis is extended over the outside 

 of the shell, though we may presume it is very thin over the 

 parts that are coloured. 



Individuals are sometimes found, — Naut. ■pompilius, j3, Gmel.; 

 List., 552; Ammonie, Montf., 74, in which the last whorl does 

 not envelope and conceal the others, but where all of them, 

 though in contact, are exposed, a circumstance which approxi- 

 mates them to the ^.mmonites; they so closely resemble the 

 common species, however, in all the rest of the shell, that it is 

 scarcely possible to believe them to be any thing more than a 

 variety of it. 



Fossil Nautili are found of a large or moderate size, and 



(1) The figure of Rumphlus is absolutely unintelligible, and it is somewhat as- 

 tonishing, that, of the many naturalists who have visited the Indian Ocean, not 

 one has ever examined or collected this curious animal, wiiich belongs to so com- 

 mon a shell. 



Vol. XL— 2 P 



