151 
AMMONITES obtusus. 
TAB. CLXVIL 
Spec. Char. Discoid, radiated; inner whorls ex- 
posed ; front with two slight furrows and an 
obtuse keel; radii large,, curved, sharpest in 
the middle ; aperture oblong. 
The large undulations or radii are equal in number to 
the septa, each crossing the inner lobes of one septum ; 
they are very prominent in the middle, but are lost after 
winding towards the front : the keel is rounded, not much 
elevated, and the hollows on the sides of it are very 
trifling. There are about four whorls ; the aperture is 
longer than wide, equalling one-third the diameter of the 
shell. I have some suspicion that the external surface of 
the shell is concentrically striated, but the specimens I 
have seen have only a small portion of it remaining. 
I am indebted to the kindness of Miss Philpot, of Lin- 
ley, for the use of the larger specimen, which, from the 
high polish and rich colour of the crystallized Carbonate 
of Iron that has lined its chambers, is truly beautiful. 
The one I have taken my section from was sent me by my 
friend Strangeways, Esq. They are both from 
Lyme, in Dorsetshire. 
