PLATE XX. 



PlSlDIUM PKKSOSATUM, Malm. 



1. External right aspect of a pair from Fitton Hall, Oldham, Lancashire. 



2. of a pair from Bassenthwaite, Cumberland. 



3. a-cl. of four pairs from Lough Fern, Co. Donegal. 



4. a, b. Posterior and dorsal view of a pair from Barnes Common, Surrey. 



5. ft, b. of a pair from Lancaster. (" P. nitidum var. splendens") 



6. a, b. of a pair from Fair Head, Co. Antrim. 



7. 0, b. of a pair from Colchester (?), Essex. 



8. a, b. of a pair from Ziegenhals, Silesia. 



9. a-l\ External aspect of a series of valves from the Holocene of the Kennet 



Valley, Berkshire. 

 10. External right aspect of a pair from Barnes Common, Surrey. 



12. of a pair from Meigle Moss, Selkirk. 



13. of a pair from Hoe Moor, Hants. 



14. of a pair from Borough Pond, Mortehoe, Devon. 



15. External aspect of four valves from the Post-tertiary deposit at Copford, 



Essex. 



16. External right aspect of a pair from Lancaster. (" P. nitidum, var. 



splendens") 



17. of a pair from Fair Head, Co. Antrim. 

 ] 8. of a pair from Colchester (?), Essex. 



19. of a pair from Ziegenhals, Silesia. 



20. a-j. Internal aspect of a series of pairs from Bishopthorpe, York. 

 20*. a, b. of a pair from Bassenthwaite, Cumberland. 



21. a, b. of a pair from Borough Pond, Mortehoe, Devon. 



22. a, b. of a pair from Meigle Moss, Selkirk. 



23. a, b. External aspect of two valves from the Pleistocene at Clacton, Essex. 



24. Diagrammatic enlargement of the Hinge. 



25. a, b. Internal aspect of a pair from Lancaster. (" P. nitidum, var. splendens.") 



26. a-j. of a series of valves showing variation, from the Holocene of the 



Kennet Yalley, Berks. 

 26*. or, fc. of two valves from the Post-tertiary deposit at Copford, Essex. 



27. a, o. of a pair from Menstrup, Sealand. 



28. a, b. of a pair from Fitton Hall, Oldham, Lancashire. 



29. a, b. of a pair from Hoe Moor, Hants. 



30. a-d. of four valves from the Pleistocene at Clacton, Essex. 



[rt is abnormal.] 



31. rt, b. of a pair from Colchester (?), Essex. 



32. or, b. of a pair from Barnes Common, Surrey. 



33. , b. of a pair from Lough Fern, Co. Donegal. 



34. c, b. of a pair from Fair Head, Co. Antrim. 



35. , b. of a pair from Ziegenhals, Silesia. 



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

 shows the amotmt of magnification. 



