PLATE X. 



PISIDIUM AST.VUTOIDES, Sandbcrgcr. 



1. a-j. External aspect of a series of valves of different ages, 



showing variation in outline and sculpture, from 

 the Pleistocene at Crayford-Erith, Kent. 



2. a-g. from the Pleistocene at Clacton, Essex. 



3. a-l. from the Pleistocene at Grays, Essex. 



4. a-j. from the Cromerian (peat) at West Kunton, Norfolk. 



5. a, 1). Posterior and dorsal view of two apposed valves from the 



Pleistocene at Grays, Essex. 



6. , b. of a pair of valves from the Cromerian at West 



Run ton, Norfolk. 



7. Umbonal view of a right valve from the same formation 



and locality, greatly enlarged to show the character- 

 istic sculpturing. 



8. a-c. External aspect of three right valves from the same forma- 



tion and locality. 



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

 shows the amount of magnification. 



