EXPLANATION OP PLATES. 



Fkontispiece. 

 TJtiio margaritifer, and pearl. 



Plate I. 



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



2. Hinge of the shell. 

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



4. Hinge of the shell. 

 5. Unto jnctorum, showing both orifices and the foot. 



6. Hinge of the shell. 



Plate H. 



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

 2. Hinge of the shell. 

 3. Dreissena polynwrpha, showing the two orifices and tubes 

 in an inverted position and the byssus attached to the 

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

 of hinge. 



Plate HI. 



Figure 1. Neritiyiajluviatilis, 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. JBifthinia tentaculata. 8. Shell, showing the operculum 

 in situ. 9. Back view of shell. 



10. Hydrohia siinilis. 11. Shell, showing the operculum m 

 situ. 12. Natural size. 



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

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



Plate TV. 



Figure 1. Planorhis corneiis, 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. Limncea peregra, showing the respiratory opening to the 



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

 11, 12. Ana/lus Jiuviatilis, showing the front and under 



side. 13, 14. SheU. 



