AMMONITES. 355 



and may be seen projecting from the surface. The Ammonites, 

 commonly called Snake-stones, are among the most abundant 

 of all fossils ; especially in the Lias, 

 Chalk, and Oolite formations. Their 

 size is sometimes very considerable ; 

 Ammonites being occasionally met 

 with of as much as four feet in dia- 

 meter ; and a diameter of three feet 

 being by no means uncommon. In 

 some places they are so numerous, 

 that the rocks seem (as it were) 

 composed of them alone. Above two 



hundred species of these shells have been already described ; and 

 it appears that many of these were very widely distributed. 

 Thus two species of Ammonites found in the Himalaya moun- 

 tains, at a height of 16,000 feet above the sea, are identical with 

 species which are common 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 Rhyncolites, 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 ( 892), 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. The shells of the Ammonites seeming to have been 

 thinner than those of the Nautilites ; and as their form was less 



