EXPLANATION OF PLATES. 



PLATE I. 



Diagrammatic Enlargements of the Hinges of : 



1. Pisidium amnicum. 



2. astartoides. 



3. casertanum. 



4. - from Caserta. 



5. [= P. fossarinum, Clessin]. 



6. ; lake, or still- water form. 



7. - personatum, 



8. pusillum. 



9. nitidum. 



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. 



