PLATE XXII. 



PlSIDIUM SUBTRUNCATUM, Malm. 



1. -/. Internal aspect of three pairs showing variation, from 



the Six-mile-water, Antrim. 



2. a, b. of a pair from the Avon at Salisbury, Wiltshire. 



3. a, b. of a pair from Drum Bridge, Lagan, Co. Antrim. 



4. a, b. of a pair from Catford, Kent. 



5. a-y. of three pairs and a left valve from Ranmore 



Common, Surrey. 

 0. a, b. of a pair from Rhosneigr Anglesey. 



7. a, b. of a pair from Bracebridge, Warwickshire. 



8. a, b. of a pair from Lochtnaben, Dumfriesshire. 



9. a, b. . of two valves from the Holocene of the Lea Valley, 



London. 



10. a, b. of four valves from the Pleistocene at West Wit- 



tering, Sussex. 



11. of a right valve from the Holocene of the Lea 



Valley, London. 



12. of a left valve from the Pleistocene at Swanscombe, 



Kent, 



13. a-c, of three valves from the Holocene at Ncwbury, 



Berks. 



14. a, b. of two valves from the rejectamenta of the Thames 



at Chertsey Mead, Surrey. 



15. Diagrammatic enlargement of the Hinge. 



16. Posterior and dorsal view of a pair from the Red Bridge 



Pond, Hampstead Heath, London. 



17. of a pair from the Six-mile-water, Antrim. 



18. a, b. External right aspect of two pairs from the Red Bridge 



Pond, Hampstead Heath, London. 

 ' ' a ' ' L of three pairs from Six-mile-water, Antrim. 



21. a-h. External aspect of a series of four pairs from Raumore 



Common, Surrey. 



22. a, b. of a pair from Bracebridge, Warwickshire. 



23. External right aspect of a pair from the Avon at Salis- 



bury, Wiltshire. 



24. of a pair from Catford, Kent. 



25. of a pair from PJiosneigr, Anglese}*. 



26. of a pair from Gloucester. 



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

 shows the amount of magnification. 



