PLATE XII. 



Fig. 



la and b. Ammonites Austeni ; reduced to one third its natural diameter; from the Grey 



Chalk of Guildford ; in the British Museum. 



2. Ammonites Austeni ; a young specimen, reduced to one half its diameter ; from the 



Grey Chalk of Sussex ; in the collection of Henry Catt, Esq. 



3. Ammonites planulatus ; from the Grey Chalk near Lewes; formerly in the collection 



of Dr. Mantell, and now in the British Museum; it is the original 

 specimen figured in the ' Mineral Conchology ;' the parts marked R are 

 restored by the artist. 



4a, b, and c. Ammonites planulatus ; an internal cast from the Upper Green Sand near 

 Cambridge ; in the collection of Mr. L. Barrett. 



