PLATE XXIV. 



Fig. 



la, b. Aptychus leptophyllus ; from the Upper Chalk of Brighton ; in Mr. Sharpe's 

 collection (Geol. Soc), p. 55. 



la, concave (internal) surface. 



lb, smooth, convex surface. 



2, 3, 4. Aptychus Portlockii ; from the Upper Chalk of Norwich ; 2 and 3 in the col- 

 lection of Mr. Bayfield ; 4 in the British Museum, p. 56. 



5. Aptychus Gollevillensis ; Upper Chalk, Norwich ; in the collection of Mr. Bayfield, 



p. 56. 



6. Aptychus Portlockii ? p. 56. 



7. Aptychus Icenicus ; Upper Chalk, Norwick; Mr. Bayfield, p. 57. 



8a, b, and 9. Aptychus rugosus; Upper Chalk, Norwich, p. 57. 



8a, external, sculptured surface of a pair of valves ; in the collection of Mr. 



Bayfield, p. 57. 

 8b, internal surface, showing lines of growth. 

 9, external surface of a large valve, in the collection of Mr. John King, of 



Norwich, p. 57. 



10a, b. Aptychus peramplus; Upper Chalk, Norwich; Mr. Bayfield, p. 58. 

 [Oa. internal, striated surface. 

 103, external surface of a fragment. 



11. Outline of the aperture of Ammonites Icenicus. 



1 2. „ „ A. Portlockii. 



13. „ „ A. leptophyllus. 



14. „ „ A. peramplus. 



15. „ „ A. Gollevillensis. 



