356 AMMONITES. 



diameter ; and a diameter of three feet being by no means un- 

 common. In some places they are so numerous, that the rocks 

 seem (as it were) composed of them 

 alone. Above five hundred species 

 of these shells have been already de- 

 scribed ; and it appears that many of 

 these were very widely distributed. 

 Thus two species of Ammonites found 

 in the Himalaya mountains, at a 

 height of 16,000 feet above the sea, are 

 exactly like species which are com- 



T . Tk l mi FIG ' 619. AMMONITE. 



mon near Lyme in Dorsetshire. These 



animals must have evidently been very important agents, their 

 carnivorous habits being duly considered, in keeping the balance 

 among the other tenants of the seas, by preventing the excessive 

 multiplication of Crustacea, as well as (in all probability) of 

 other Mollusks, and of Fishes. That their mouth was armed 

 in the same manner as that of the existing Cephalopods, is 

 evident from the fact, that Rhyncholites, or fossilized beaks, are 

 found in large numbers, associated with the shells of the Ammo- 

 nites, in the beds in which they occur. It has been suspected 

 by some Naturalists, that the Ammonite might have been, like 

 the existing Spirula ( 964), an internal, not an external, shell. 

 This idea, however, is inconsistent with the size of the outer 

 chamber, which is quite large enough to receive the animal, 

 usually forming two-thirds of an entire whorl or turn of the 

 shell; and also with the fact that the mouth of the shell, in 

 specimens in which it has been found perfect, is so constructed 

 as to have been evidently connected with the external parts of 

 the animal, and not to have furnished attachment to internal 

 organs. According to Mr. Woodward, also, there is a specimen 

 of an " Ammonite in the British Museum, evidently broken and 

 repaired during the life of the animal, which shows that the 

 shell was deposited from within" The shells of the Ammonites 

 seeming to have been thinner than those of the Nautilites, and 

 their form being less arched, they would have been less capable 

 of resisting pr^ure if they had not been furnished with ribs and 



