PLATE XXI. 



PISIDIUM PUSILLUM, (Gmelin) Jenyns. 



1 . a-e. External aspect of a series of pairs from Bracebridge, Warwickshire. 



2. of a pair from the Botanical Gardens, Naples. 



3. of a pair from Sutton Coldfield Park, Warwickshire. 



4. a, b. Posterior and dorsal view of a pair from Bracebridge, Warwickshire. 



5. rt, b. of a pair from Kilcorrig, Lisburn, Co. Antrim. 



0. , b. of a pair from Woodburn Dam, Co. Antrim. 



7. , b. of a pair from Walworth Wood, Co. Londonderry. 



8. a, b. of a pair from Comber, Co. Down. 



9. a, b. of a pair from the Holocene at Magheragera, Co. Fermanagh. 



10. a-c. External aspect of three right valves from the Holocene at Westbury- 



on-Severn, Gloucestershire. 



11. a-f. right aspect of a series of six pairs from Woodburn Dam, Co. Ant rim. 



12. a-d. of a series of four pairs from the Holocene of the Lea Valley, 



London. 



13. of a pair from Tenby, Pembrokeshire. 



14. of a pair from Comber, Co. Down. 



15. of a pair from Walworth Wood, Co. Londonderry. 



16. of a pair from the lliver Po, Italy. 



17. ci-7i. External aspect of a series of valves showing variation, from the Pleisto- 



cene at Swanscombe, Kent. 



18. , b. External right aspect of two pairs from Magheragera, Co. Fermanagh. 



19. of a pair from llhosueigr, Anglesey. 



20. of a pair from Kilcorrig, Lisburn, Co. Antrim. 



21. Diagrammatic enlargement of the Hinge. 



22. a-d. Internal aspect of four valves from the Holocene at Ncwbury, Berks. 



23. a-e. of five valves from the Holocene at West bury -on-Severn, Gloucester- 



shire. 



24. --/. of five pairs from Woodburn Dam, Co. Antrim. 



25. a-k. of a series of pairs from Bracebridge, Warwickshire. 



26. a, b. of a pair from Ealing, Middlesex. 



27. a-d. of four valves from the rejectamenta of the Thames at Chcrtsey 



Mead, Surrey. 



28. a-f/. of a series of valves from the Holocene of the Lea Valley, London. 



29. a-d. of two pairs from the Botanical Gardens at Xaples. 



30. a, b. of a pair from Kilcorrig, Lisburn, Co. Antrim. 



31. rt-7/. of four pairs from Magheragera, Co. Fermanagh. 



32. a-f/. of a series of valves from the Pleistocene at Swanscombe, Kent. 



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



34. , b. of a pair from the River Po, Italy. 



35. a, b. of an abnormal pnir from Walworth Wood, Co. Londonderry. 



36. a, b. of a pair from Willenhall, Staffordshire. 



37. o, b. of two valves from the Cromerian (peat) at West Runton, Norfolk. 



38. r/, b. of a pair from Comber, Co. Down. 



39. o, b. of a pair from Walworth AVood, Co. Londonderry. 



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



41. a, b. of two valves from the Pleistocene at West Wittering, Sussex. 



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

 shows the amount of magnification. 



