65 
AMMONITES serratus* 
TAB. XXIV, 
Spec. Char. Involute., depressed, carinated, inner 
whorles two-thirds concealed ; surface radiated 
and undulated near the circumference ; keel dis- 
tinct, sharply crenated, containing the siphun- 
cuius; aperture narrow, five-angled, half the 
diameter of the shell in length. Volutions five. 
Diameter four inches, thickness one inch. The sides 
of the whorles are rather concave near the keel, which is 
nearly cylindrical, and from the sharpness of its crenatures, 
may almost be called serrated or jointed. The septa are 
close, with many deep undulations on their margins. 
I do not know that this species has ever been found 
perfect. The upper specimen retains some of the shell 
in one part very perfectly ; we see in it also part of one of 
the divisions of the shell prettily spreading into the small 
external sutures, and exposing the passage or hole of the 
siphunculus belonging to the turn within it; where the 
shell is lost, the various undulating ramifications, which 
have a kind of foliage-form, more or less perfect, are 
explained. 
The under figure shows the frequent divisions, and that 
there are about five rather distinct principal undulations, 
which divide alternately, and lock into smaller sutures. 
