PLATE XI. 



PISIDITJSI ASTAKTOIDES, Sandbcrger. 



1. -n. External aspect of a series of valves showing variation in 



the outline and sculpture, from the Cromerian 

 (gravel) at West Run ton, Norfolk. 



2. a-p. from the Pleistocene at Swanscombe, Kent. 



51s** The scale in millimetres under each figure, or series of figures, 

 shows the amount of magnification. 



