PLATE XX. 



Fig. 



la, b, c. Ammonites rusticus ; from the Lower Chalk, near Lyme Regis ; in the Museum 

 of Practical Geology; reduced to two thirds its natural diameter, p. 44. 

 The surface of the inner part has decayed away. 



la, side view. 



Id, back view. 



lc, section of the outer whorl. 



2a, b, and c. Ammonites Renevieri ; from the Grey Chalk, near Blackdown, Isle of 

 Wight; in the collection of E. Renevier, Esq., of Lausanne, p. 44. 

 2a, side view. 

 2b, front view. 

 2c, outline of a septum. 



3a and b. Ammonites Saxbii ; from the Grey Chalk of Ventnor, Isle of Wight ; in my 

 possession, p. 45, 

 3a, side view. 

 3b, front view. 



4a and b. Ammonites Vectensis ; from the Chloritic Marl of Ventnor, Isle of Wight ; in 

 my possession, p. 45. 

 4a, side view. 

 4<5, front view. 



