PLATE XXVII. 



PISIDITTM SUPIKTJM, A. Schmidt. 



1 . a-q. 1 Internal aspect of a series of valves of all ages showing 



2. a-x. / variation, from the Pleistocene at Grays, Essex. 



PJSIDIUM PAKVTTLTJM, Clessin. 



3. a-b. Posterior and dorsal view of a pair ^ ., 



. from Forsoen, 



4. External right view ol a pair 



5. a-b. Internal aspect of a pair 



6. Diagrammatic enlargement of the Hinge. 



Denmark. 



PISIDITJM VINCENTIATSTJM, B. B. "Woodward, n. sp. 



7. Diagrammatic enlargement of the Hinge. 



8. a-b. Posterior and dorsal aspect of apposed 1 from the 



valves 



Campinien 



9. a-/. External aspect of a series of valves } (Pleistocene) 



" \ Internal aspect of a series of valves 

 11. a, b. ) ) Belgium. 



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

 shows the amount of magnification. 



