134 
AMMONITES undatus. 
TAB. DLXI X.—Jig. 2. 
Spec. Char. Discoid,, smooth,, with a rounded edge; 
whorls flat on their sides, their inner edges 
square ; inner whorls partly visible ; aperture 
much elongated, sagittate., with obtuse angles ; 
edge crossed by undulations which proceed a 
short way over the sides. 
A very flat Ammonite, distinguished from all others by 
the undulations over the edge and square inner margins 
of the whorls. 
This rare specimen was presented to my father in 
1820, by G. A. Mantell, Esq., who obtained it from the 
Upper Chalk of Sussex. 
AMMONITES Bakerim. 
TAB. DLXX.—^g’s. 1. & 2. 
Spec. Char. Depressed, radiated ; inner whorls 
exposed ; radii curved, furcate, continued over 
the front ; whorls crossed by about ten sinuous 
lines ; aperture oblong. 
The peculiarity of this Ammonite consists in the sinuous 
lines that mark its surface, and probably indicate suc- 
cessive periods when the edge of the aperture was com- 
pleted and the growth for a while suspended, although 
