153 
AMMONITES falcatus. 
TAB. DLXXIX.— fig. 1. 
Spec. Char. Discoid,, subumbilicate, radiated ; 
whorls crenated and flat at both edges, the in- 
ner ones almost concealed ; radii falciform, 
bent in the middle ; aperture sagittate with 
truncated angles. 
Syn. A. falcatus. Mantell Geol. Suss.p. 17. tab . 21. 
/. 6 . & 12 . 
a This rare and elegant species is almost flat, the long- 
est diameter exceeding its greatest thickness nearly four- 
fifths. The volutions are slightly enlarged in the centre, 
but are contracted at the ambit .... with delicate pli- 
cated edges. The radii are very slender at their origin 
in the umbilicus, but gradually increase in breadth; and 
passing obliquely to the centre of the volutions, make a 
sudden curve towards the margin, where they terminate 
in obtuse folds.” The front is very narrow and flat ; the 
cast of it shows a furrow along the middle in which the 
siphuncle was placed. 
I am indebted to Mr. Mantell for permission to figure 
his best specimen, which was found at Middleham in 
Gray Chalk Marl. 
