150 



the animal might overlap and surround the mouth of the shell : a dis- 

 covery which cannot fail to throw light on the economy of many of the 

 inhabitants of the minute multil ocular shells. Lamarck considering 

 that, agreeable to the discoveries of M. Peron, three fourths of the shell 

 of Spirilla is covered by the animal, and that there is great reason to sup- 

 pose that one third of the shell of the Nautilus is also thus covered, is of 

 opinion, that the nummulite was completely inclosed in the posterior 

 part of the animal by which it was formed ; and that a part of the 

 extremity of the animal was contained in, and was adherent to, the last 

 chamber. 



Possessing several small masses of these bodies, and having been care- 

 ful in collecting all the different surfaces and forms under which these 

 bodies presented themselves, in different specimens, I made a careful 

 examination of them, with the hope of obtaining some more particular 

 information respecting their original nature. 



The size of the specimens, which I possess, vary in their diameter, 

 from less than an eighth of an inch to an inch and a quarter; and I am 

 satisfied, that I once had some which were full an inch and a half in 

 diameter. In thickness, they vary from an eighth of an inch to half 

 an inch. 



Their figure is in general lenticular. Considerable variations, how- 

 ever, are frequently observable in this respect ; the lens, from what has 

 been stated in the preceding paragraph, being much deeper in some 

 l.han in others : some, indeed, being nearly flat, whilst others are even 

 almost globular. In some, a considerable deviation appears to have 

 taken place from their original figure, from their having become bent 

 in various ways. The surface varies considerably in different specimens ; 

 being in some nearly smooth, in others rough and scabrous, with nu- 

 merous small projecting knobs, or undulating lines. Their colour is also 

 various ; some being white, some of different shades of brown and red, 

 and others even of a blueish hue; and the difference of colour is certainly 

 not always dependent entirely on the nature of the matrix in which 



