EXPLANATION OF PLATES. 



FRONTISPIECE. 

 Unio margaritifer, and pearl. 



PLATE I. 



Figure 1. Sphcerium rivicola, showing the double tube and foot. 



2. Hinge of the shell. 

 3. Pisidium amnicum, showing the single tube and foot. 



4. Hinge of the shell. 

 5. Unio pictorum, showing both orifices and the foot. 6. Hinge 



of the shell. 



PLATE II. 



Figure 1. Anadonta anatina, showing both orifices and the foot. 

 2. Hinge of the shell. 



3. Dreissena polymorpha, showing the two orifices and tubes 



in an inverted position and the byssus attached to the 

 fragment of a valve of an Anatina. 4. Shell. 5. Inside 

 of hinge. 



PLATE III. 



Figure 1. Neritina fluviatilis, showing the snout, tentacles, position 



of the eyes, and the foot. 2. Shell. 3, 4. Operculum. 

 5. Paludina vivipara. 6. Shell, showing the operculum in 

 situ. 



7. Bythinia tcntaculata. 8. Shell, showing the operculum in 



situ. 9. Back view of shell. 



10. Hydrobia similis. 11. Shell, showing the operculum in situ. 



12. Natural size. 



13. Valvata cristata, showing the branchial plume and filament. 

 14. Shell of V. piscinalis. 15. Operculum of same. 



PLATE IV. 



Figure 1. Planorbis corneus, showing the body and attachment of the 

 foot. 2, 3. Shell. 



4, 5. Physa fontinalis, showing the digitated lobes of the mantle. 



6, 7. Shell. 



8. Limncea peregra, showing the respiratory opening to the right. 



9, 10. Shell of L. stagnalis. 



11, 12. Ancylus fbuviatilis, showing the front and under side. 



13, 14. Shell. 



