hamstead beds. 



185 



Fig. 68. 



Cerithium plicatum, 

 Lam. 



Fig. 69. 



Corhula pisum, 

 Sow. 



Fig. 70. 



Cerithium elegans, 

 Desb. 



Fig. 71. 

 Corhula vectensis, Forbes. 



The line between the 



This classification might with ad- 

 vantage be considerably simplified. 

 The Corhula Beds and Cerithium 

 plicatum Beds pass imperceptibly into 

 each other, and form one marine divi- 

 sion, with Corhula becoming scarcer 

 below, and Cerithium dyino- out 

 above. In fact, these strata become 

 more truly marine upwards, though 

 Corhula vectensis (Fig, 7l) extends 

 downwards even to the base of the 

 marine bands. 

 Middle and Lower Freshwater and 



Estuary Marls is a very indefinite one, and proves to be only of 

 local value, for the White Band, which Forbes took as the 



junction, soon dies out and there is no palaeontological evidence on 

 which to separate the two horizons."^ 



The Hamstead Beds may therefore be divided into : — 



Marine Beds, with Corhula, Cytherea, Ostrea 

 callifera, Cuma, Valuta, Natica, Cerithium, and 

 Melania - - - - _ 



Freshwater, estuarine, and lagoon beds, with 

 Unio, Cyrena, Cyclas, Paludina, Hydrohia, 

 Melania, Planorhis, Cerithium (rare). Turtles, 

 Crocodiles, Mammals, Leaves, and Seeds 



Feet. 



31 



225 



256 



* Melania fasciuta seems to be only a stunted form of M. infiata. Selected 

 specimens are sufficiently different, but certain beds contain forms that miffht be 

 referred to either. 



