PLATE XXIII. 



PISIDIUM PULCHELLUM, Jenyns. 



External right aspect of two pairs from Comber, Co. Down. 



- of a pair from Aldenham, Hertfordshire. 



- of a pair from Denham, Buckinghamshire. 



- of a pair from Harefield, Middlesex. 



Posterior and dorsal view of a pair from the same locality. 



- of a pair from' Bracebridge, Warwickshire. 

 - of a pair from Walworth, Co. Londonderry. 



External right aspect of two pairs from the same locality. 



- of a valve from the Holocene of the Lea Valley, London. 



- of a valve from the Holocene in Berkshire, near Statues. 



- of a series of pairs from Bracebridge, Warwickshire. 

 Internal aspect of another series from the same locality. 

 Diagrammatic enlargement of the Hinge, 



External right aspect of a valve froin the Pleistocene at West Witt 



Sussex. 

 Internal aspect of a series of valves from the Holocene of the Lea V 



London. 

 of a pair from Comber, Co. Down. 



- of a pair from Walworth, Co. Londonderry, 



- of two valves from the Holocene in Surrey, near Staiues. 



- of a pair from the Coin, West Drayton, Middlesex. 



- of a pair from Denham, Buckinghamshire. 



PISIDIUJH LiLLJEBORGii, Clessin. 



2. External right aspect of a pair from Silvercjale, Lancashire. 



18. a, b. Internal aspect of another pair from the same locality. 



[These figures are placed here for comparison with those < 

 foregoing species for which P. lilljeboryii has sometimes been misti 



PISIDIUM HEKSLOWANUM, Sheppard. 



21. External right aspect of a pair from the Avon at Salisbury, Wiltsl 



22. a-c. External aspect of three pairs from the Wendover Canal, li ticking 



shire. 

 External right aspect of two pairs from Sutton Coldfield, Warwick 



- of a pair from Berkhampstead, Hertfordshire. 



External aspect of two very young valves from the Holoceno at ] 

 bijrgh, Suffolk, to show the position at this age o 

 appendiculae. (Of. also 29 c & d.) 

 Posterior and dorsal views of apposed valves from the Pleistoc* 



Crayford-Erith, Kent. 



-- of a pair from the Red Bridge Pond, Hampstead Heath, Lom 

 External right aspect of another pair from the same locality. 

 Posterior and dorsal view of a pair from Bagnley, Cheshire. 

 External aspect of a series of valves of all ages showing variation, 



the Pleistocene at Crayford-Erith, Kent. 

 [ & t are examples of the fractured and repaired valves whi 

 not uncommon in the deposit.] 



- of a series from the Pleistocene at Swanscombe, Kert, 



- of a similar series from the Pleistocene at Clacton, Essex. 



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

 allows the amount of magnification. 



