80 



AMMONITES Lewesiensis. 

 TAB. CCCLVIIl. 



Spec. Char. Discoid, obscurely radiated, radii 

 large and obtuse ; whorls depressed, inner 

 ones half exposed ; front narrow, rounded, 

 plain ; aperture sagittate. 



Syn. a. Lewesiensis. Mantell, Fossils of the 

 South Doivns, p. 199, tab. 22, /. 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 Mantell, Esq. whose 

 zeal for science has not been checked by the weight of 

 the masses that have fallen in his way, or the difliculty 

 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- 



