80 
AMMONITES Lewesiensis. 
TAB. CCCLVII1. 
Spec. Char. Discoid, obscurely radiated, radii 
large and obtuse ; whorls depressed, inner 
ones half exposed ; front narrow, rounded, 
plain ; aperture sagittate. 
Syn. A. Lewesiensis. At ant ell, Fossils of the 
South Downs , p» 199, tab. 22, f. 2. 
So rapidly do the volutions of this shell increase in size, 
that it has the appearance of being umbilicated, although 
about half of the inner whorls is visible. The breadth of 
the last whorl, or what is the same thing, the length of 
the aperture, seldom, as far as I have had an opportu- 
nity of observing, equals half of the diameter, although 
one of the three proportions given in Mr. Mantell’s de- 
scription, makes it equal to 9-14ths, possibly pressure 
may make as much irregularity in the proportions as are 
observable in different parts of that description, evidently 
taken from several individuals. The radii are broad, 
very little elevated, and often entirely obliterated, in 
which latter case the edges of the septa become beauti- 
fully develloped. 
Several varieties of this gigantic Ammonite have been 
sent me from Lewes, by Gideon Mantel], Esq. whose 
zeal for science has not been checked by the weight of 
the masses that have fallen in his way, or the difficulty 
of their removal. I have given a diminished figure of a 
specimen fifteen inches in diameter and four inches thick, 
which has lost, almost entirely, the obtuse radii, a cir- 
