352 BELEMNITES. ORDER TETRABRANCHIATA. 



covery of specimens of Belemnites, in which the soft parts of the 

 animal are so well preserved, as to enable their form and general 

 structure to be distinctly traced. From these it has been ascer- 

 tained, that the arms were furnished with hooks, as in the Ony- 

 choteuthis ; and that the body had a pair of small lateral fins 

 situated at about the middle of its length. From the weight of 

 its dense internal shell, the Belemnite may be supposed to have 

 commonly maintained a vertical position ; and, as its chambered 

 portion was provided with a siphuncle analogous to that which 

 we find in the Nautilus ( 966), the animal probably had the 

 power of ascending and descending in the water with facility. 

 It would rise swiftly and stealthily to fix its claws in the belly 

 of a fish swimming at the surface above ; and then, perhaps, as 

 swiftly dart down and drag its prey to the bottom, and devour it. 

 We cannot doubt that, like the hooked Calamaries of the present 

 seas, the ancient Belemnites were the most formidable and pre- 

 daceous of their class. 



ORDER IL TETRABRANCHIATA. 



966. From the remains preserved in a fossil state, the Cepha- 

 lopoda of this Order appear to have been formerly most abund- 

 ant in our seas ; as they present themselves throughout almost 

 all marine strata, from the very earliest of the Palaeozoic series, 

 to those of a comparatively recent epoch. Yet some causes, of 

 which we are at present ignorant, have produced the almost 

 entire extinction of the Order ; the only existing representatives 

 of it being the well-known Nautilus pompilius, or Pearly Nau- 

 tilus, so named from the nacreous lining of its shell, and two or 

 three allied species. The shell of the Nautilus is well known ; 

 being found on most shores between the tropics. Of the animal 

 which constructs it, however, Naturalists had, until recently, the 

 most vague and incorrect ideas, the Nautilus being very rarely 

 met with in the living state, owing to its being an inhabitant of 

 the open sea, and possessing the power of sinking at the slightest 

 alarm. The general structure of the shell, which may be taken 



