AMMONITES Walcotii. 
TAB. CVI. 
Spec. Cuar. Involute, depressed; volutions four, 
three-fourths exposed, with a concentrate fur-~ 
row; lunate undulations over half the sides; 
front with a carina between two furrows. 
en PI ee 
Aventure oblong, its length equal to one-third of the 
diameter of the shell: the sides are flatted; each whorl is 
divided into two parts by an obtuse furrow; the inner half 
is nearly smooth, the other marked by semi-lunar depressions. 
This species is much spread about; I have it in ferru- 
ginous marly Limestone from near Bath—from Llantrissant 
near Cardiff by favour of Miss Hill—and from White 
Lackington Park. I have specimens marked Devonshire 
and River Trent. It is abundant in clayey Ironstone or 
black marle at Colebrook dale, with blend or black Sul- 
phuret of Zinc, and included in balls in the dark pyrit- 
aceous or Alum Clay at Whitby. 
The species generally runs from two to four inches in 
diameter; the shell is laminated and scaly, composed of 
two, three or more coats, and rather deep, yet the sutures 
of the septa continue to near the outside, and the form is 
the same throughout the cast, differing from the outside 
ornament or pattern only in the greater depth of the furrow. 
The insides are divided by various crystallizations of Car- 
bonate of Lime or Iron, or more solid or earthy, and more 
