PLATE XIX. 



PiSIDIDM XITIDTM, JenyilS. 



1. a, b. External right aspect of two pairs from Swinton, Lancashire. (T. ' 



coll.) 



2. of a pair from Truro. Cornwall. ((). Boettger.) 



3. of a pair from Button Colclfield Park, Warwickshire. 



4. r(, b. Posterior and dorsal view of a pair from Ten by, Pembrokeshire. 



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



6. a, b. of a pair from Swinton, Lancashire. (T. llogers coll.) 



7. a, b. of a pair from the Holocene of the Lea Valley, London. 



8. External right aspect of a pair from Hoe Moor, Hampshire. | 



iateralu.") 



9. of a pair from Louth, Lincolnshire. 



10. of a pair from Church Close, Mortehoe, Devon. 



11. of a pair from Lough Fern, Co. Donegal. 



12. , b. of two pairs from Deutschbrod, Bohemia. 



13. of a pair from Tenby, Pembrokeshire. 



14. of a pair from Gt. Gaddesden, Hertfordshire. 



15. a, b. of two pairs from Lochmahen, Dumfriesshire. 



] 6. Diagrammatic enlargement of the Hinge. 



17. , b. Internal aspect of a pair from Swinton, Lancashire. (T. Rogers 



18. a, b. of a pair from Hoe Moor, Hants. (" Var. laUrali*"} 



39. a, b. of a pair from Tenby, Pembrokeshire. 



20. a-d. of two pairs from Lochmaben, Dumfriesshire. 



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



22. a-c. of a pair and a left valve from Church Close, Mortehoe, Dev 



23. a-d. of two pairs from Deutschbrod, Bohemia. 



24. a, b. of a pair from Truro, Cornwall. (0. Boettger.) 



25. o, b. of a pair from Louth, Lincolnshire. 



26. a-d. of four valves from the Holocene in Surrey, near Staines. 



26*. a, b. of two valves from the Holocene of the Lea Valley, London 



27. of a right valve from the Holocene at Newbury, Berks. 



28. a, b. of two valves from the Holooene at Clifton Hampden, Oxfor 



29. a, b. of a pair from Sutton Coldfield Park, Warwickshire. 



30. a-y. External aspect of a series of valves showing variation, frc 



Pleistocene at Swanscombe, Kent. 



31. , b. of two valves from the Holocene at Clifton Hampden, Oxfor 



32. of a right valve from the Holocene at Newbury, Berks. 



33. , b. of two valves from the Holocene in Surrey, near Staines. 



34. a-f. Internal aspect of a series of valves from the Pleistocene at Swans 



Kent. 



35. </, b. of two valves from the Pleistocene at West Wittering, Sussi 



36. a-d. of four valves from the Cromerian (peat) at West Ihinton, N 



37. a, b. of a pair from Gt. Gaddesden, Hertfordshire. 



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

 shows the amount of magnification. 



