Lamarck's Genera of Shells, 247 



tion of the last whorl seems to be enveloped by the posterior part 

 of the sack or mantle of the cephalopodous animal to which it be- 

 longs, the remainder of the shell being uncovered and visible ; 

 whilst another part of the animal is contained in the last chamber 

 of the shell, to which it probably adheres by a tendinous ligament, 

 inserted in the extremity of the siphon *. The want of colour at 

 the end of the last whorl, confirms this supposition. 



Type. Nautilus pompiliust. (Idem. Linn.') 



Shell suborbicular, marked with red streaks ; whorls smooth at 

 the back and sides; aperture oblong-cordate ; umbilicus concealed. 

 Indian Ocean. PI. vi. Fig. 230. 2 Species, both recent. 

 7th Family. 

 Ammoneata. (5 genera.) 



Septa sinuous, lobed and indented at the circumference, united 

 at the inner surface of the shell, and articulating with it by means 

 of indented sutures. 



The multilocular shells of this family are very remarkable for 

 the character of their septa, whose wavy and sinuous discs, lobed 

 and indented at their circumference, form, by their union, as they 

 fold back at their junction with the inner surface of the shell, a 

 sort of indented sutures, not unlike the leaves of the parsley. These 

 suture sarc hidden by the exterior portion of the shell ; but, although 

 we usually find the ammoneata in the fossil state, after the shell has 

 disappeared, still their casts display, in a very evident manner, 

 the peculiar characters of the family. 



Of the animals belonging to these shells we know nothing ; but 

 from their being multilocular, we presume, with great probability, 

 that they are cephalopoda, and analogous to the nautili, though 

 at the same time very distinct from that genus. It seems probable 

 that the shell is wholly internal, and, as Bruguieres has supposed, 

 that most of them live at great depths in the ocean. 



The general form of these multilocular shells varies extremely 



* A simitar confirmation, there is every reason to suppose, must belong to 

 the ammonites, nummnlites, &c. See what has been already said on this sub- 

 ject under the head Spirula* 



t From wo|uwi>ioc, whence pompilus, a term used by Pliny, for a species of 

 nautilus. 



