56 THE AQUAVIVARIUM. 



prolific, one or two of these fellows may be put in 

 to eat it down, but they should be removed before 

 every leaf is cleared off. Another genus which 

 should be represented is that of the Marsh-Shells 

 (Paludina). Of these the beautiful Crystalline and 

 Common Marsh-Shells (P. vivipara, Fig. 22, and 



FIG. 22. 



FIG. 21. 



P. achatina) should find their way into every col- 

 lection. 



The Conchifera have fewer representatives than 

 the Gasteropoda. Almost any of them may be 

 introduced into the Aquavivarium. Several of 

 them are of large size ; the Swan Fresh-water 

 Mussel (Anodon Cygmus} is one of the largest, and 

 is a common inhabitant of ponds. The most inter- 

 esting of our fresh-water shells is the Pearl Mussel 



