PLATE IX. 



PISIUIUM AMNICTJM (Mlillcr). 



1. a-f. Internal aspect of a series of adult valves, showing 



variation in outline, of the typical form from the 

 Pleistocene at Crayford-Erith, Kent. 



2. a-h. of the " var. danubialis " from the Pleistocene at 



Grays, Essex. 



3. -/! of young valves of the typical form, from the 



4. a-f. / Pleistocene at Crayford-Erith, Kent. 



'" I of the young valves of the " var. danubialis,'" from 



the Pleistocene at Crayford-Erith, Kent. 



7. a-d. } 



[7 c contains an attached Pearl : the only instance 

 met with.] 



8. o, b. of two adult valves of the intermediate form, from 



the Cromerian at West llunton, Norfolk. 



9. a-f. - of a series of valves of the extremely triangular 



form, from the Pleistocene at Grays, Essex. 



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

 shows the amount of magnification, 



