PLATE XV. 



PlSIDIUM CASEKTA.NUM (Poll). 



1. a, It. External aspect of a pair from the type locality, Caserta. 



2. , ft. Enlargement of the Hinge of the above. 



3. a, b. Diagrammatic enlargement of the Hinge of a typical 



specimen. 



4. a, b. Enlargement of the Hinge of P. fossarhnim, Clessin. 



5. , b. Diagrammatic enlargement of the Hinge of the lake, or 



still-water form. 



6. a, b. Internal aspect of a pair of valves from Fitton Hall. 



Oldham, Lancashire. ("P. pusillum^ var. gran- 

 dis": T. Rogers coll.) 



7. rt. 1). of a pair from Gateshead, Durham. ("P. cinereum": 



T. llogcrs coll.) 



8. a, b. of a pair from Scarborough, Yorkshire. 



9. , b. of a pair from Annadale, Co. Down. 



10. a, b. of a pair from Swinton, Lancashire. ("P. fonti- 



nale, var. cinereum [sic]," marked " J. G. Jeff." : 

 T. Rogers coll.) 



11. , b. of a pair from Manchester. ("P. fontinaJe, var. 



rosea, Scholtz " from 0. Boettger.) 



12. , b. of a pair from Swinton, Lancashire. ("P. pusillum, 



large variety, J. G. Jeff." : T. llogers coll.) 



13. , b. - of a pair from Naples. (" P. australe, Phill." : 



11. Bellini.) 



14. rt, b. of a pair from Bath, Somersetshire. (" P. fontinale, 



var. pulcheUa, named by Mr. Jenyna": T. Rogers 

 coll.) 



15. a, ft. of a pair from Addington, Surrey. 



16. rt, b. of a pair from Saunton, Mortehoe, Devon. 



17. of a right valve from Trancailla, Italy. 



18. rt, b. of a pair from Sicily. (" Galileja tenebrosa, 0. G, 



Costa " : R. Bellini.) 



19. rt-7t. of a series of valves from Giesegaard, near Borup, 



Sealand. 



20. a-li. from Lyngby-Bagsvor So, Sealand. 



21. rt, b. of a pair of valves from North Wootton, Norfolk. 



22. , ft. of a pair from Tudor Hill, Sutton Coldfield, War- 



wickshire. 



23. a, ft. of a pair from Trancailla, Italy. 



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

 shows the amount of magnification. 



