ammonites were external shells. 3.37 
consequently of design, a few of W'hicli I shall 
endeavour briefly to point out. 
External Shell. 
The use and place of the shells of Ammonites 
itas much perplexed geologists and conchologists. 
Cuvier and Lamarck, guided by the analogies 
nftbrded by the Spirula, supposed them to be 
internal shells.* There is, however, good reason 
to believe that they were entirely external, and 
that the position of the body of the animal within 
these shells was analogous to that of the inha- 
bitant of the Nautilus Pompilius. (See PI. 31, 
1 ). 
* The smallness of the outer chamber, or place of lodgment 
tor the animal, is advanced by Cuvier in favour of his opinion 
that Ammonites, like the Spirula, were internal shells. This 
’’eason is probably founded on observations made upon im- 
perfect specimens. The outer chamber of Ammonites is very 
seldom preserved in a perfect state, but when this happens, it 
*s found to bear at least as large a proportion to the cham- 
bered part of the shell, as the outer cell of the N. Pompilius 
bears to the chambered interior of that shell. It often occupies 
tnore than half, (see PI. 36. a. b. c. d.) and, in some cases, 
Ibe whole circumference of the outer whorl. This open chamber 
not thin and feeble, like the long anterior chamber of the 
'Spirula, which is placed within the body of the animal producing 
•■bis shell ; but is nearly of equal thickness with the sides of 
•be close chambers of the Ammonite. 
Moreover, the margin of the mature Ammonite is in some species 
•eflected in a kind of scroll, like the thickened margin of the shell 
the garden snail, giving to this part a strength which would 
Apparently be needless to an internal shell. (See PI. 37. Fig. 3. d.) 
The presence of spines also in certain species, (as in A. 
