PLATE XXII. 

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



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



5. a~(j. -- of three pairs and a left valve from Ilanmore 



Common, Surrey. 

 G. , b. -- of a pair from Rhosneigr Anglesey. 



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



8. , b. -- of a pair from Lochmaben, Dumfriesshire. 



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



London. 



10. cr, />. 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 Newbury, 



Berks. 



14. , 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. , b. External right aspect of two pairs from the lied Bridge 



Pond, Hampstead Heath, London. 



* a ' 



20 I ~ ' Six-mile-water, Antrim. 



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



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 Ilhosneigr, Anglesey. 



26. of a pair from Gloucester. 



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

 shows the amount of magnification. 



