EXPLANATION OF PLATES. 



PLATE I. 



Diagrammatic Enlargements of the Hinges of: 



1. Pisidium amnicum. 



2. - astartoides. 



3. ca-sertanum. 



4. from Caserta. 



5. [= P. fossarinum, Clessin]. 



6. : lake, or still-water form. 



7. personatum. 



8. piisillum. 



9. nitidxm. 



10. milium. 



(Figs. 2 & 3 have been only slightly " touched.'*) 



In the above Plate the white dots are placed opposite the 

 apices of the inner lateral teeth, and in fig. 7 the two white lines 

 point towards the callus. 



