NAUTILUS undulatus. 
TAB. XL. : 
Spec. Cuar. Gibbose; surface largely undulated, 
sides rather conical, edge flat; aperture obcor- 
date, inner whorls concealed. 
— 
Tur septa are somewhat numerous, each one is crossed 
obliquely by an undulation of the surface. The thickness 
_ is half of the diameter, and the length of the mouth rather 
more, with the siphunculus near the centre. A single line 
runs along the middle of the flat part of the edge or back.* 
This species is found in a marly sandstone, a little above. 
the fullers earth at Nutfield in Surrey, it varies in size, 
- being sometimes twelve inches in diameter, forming a very 
heavy mass, being generally a mixture of Irony marle or 
clay with sand. It would appear from some that the outer 
chamber is very large, and therefore the older or larger 
shells seem to have less of the undulations. I have not 
seen any specimen resembling this from any other place, 
wherefore I might have named it Nutfieldiensis, but although 
it is characteristic of the place, I shall find that trivial name 
better suited to some other shell which is also characteristic. 
* We must be cautious of looking upon this as an indistinct siphunculus, 
as in some cases it might seem to be. 
