EXPLANATION OF PLATES. 



Frontispiece. 

 Unio margaritifer, and pearl. 



Plate I. 



Figure 1. Sphcsrium rivicola, sliowing the double tube and foot. 



2. Hinge of the shell. 

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



4. Hinge of the shell. 

 5. Uiiio pictoi'um, showing both orifices and the foot. 



6. Hinge of the shell. 



Plate U. 



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

 2. Hinge of the shell. 



3. Dreissena ])olymorpha, showing the two orifices and tubes 



in an inyerted position and the byssus attached to the 

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

 of hinge. 



Plate HI. 



Figure 1. Neritinajluviatilis, showing the snout, tentacles, position 

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

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

 situ. 



7. Bythinia tentaculata. 8. Shell, showing the operculum 



in situ. 9. Back view of shell. 



10. Hydrohia similis. 11. Shell, showing the operculum «« 

 situ. 12. Natural size. 



13. Valvata cristata, showing the branchial plume and fila- 

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

 same. 



Plate IV. 



Figure 1. Planorhis corneus, showing the body and attachment ot 

 the foot. 2, 3. Shell. 



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



mantle. 6, 7. Shell. 



8. Lirnncea pereyra, showing the respiratory opening to the 



right. 9, 10. Shell of L. stayncuis. 



11, 12. AncyJus Jiuviatilis, showing the front and imder 



side. 13, 14. Shell. 



