CHAPTER X. 



MtlSSELS. 



I HE Conchifera (shell-bearers), or Bivalves, form one 

 of the STib-diTisions of the Molluscas. They never 

 live (as so many of the gasteropods, or univalves, 

 do) upon land, but always in either fresh or salt water, most 

 of them, however, being inhabitants of the latter. The fresh- 

 water bivalves are not only useful in the aquarium, but they 

 are in themselves full of interest, and anyone who will watch 

 and study them a little will certainly be rewarded for his 

 trouble. 



Those who begin keeping aquaria are sometimes advised to 

 have nothing to do with the Conchifera, as they are so likely 

 to die and coiTupt the water. I cannot say that such has 

 been my experience, for I have rarely known them die, and 

 my tanks have never suffered any bad effects to my know- 

 ledge through their death. Nor are they likely, as far as I 

 know, to do any harm by their slowly ploughing through the 

 sand and gravel at the bottom of the aquarium. As a rule, 

 they are useful as scavengers, for they extract from the water 

 particles of animal and vegetable matter. They are exceedingly 

 prolific, and, breeding readily in confinement, their eggs and 

 fry supply the fish with suitable food. Some bivalves of 

 course are more active than others. For example, some of the 

 Sphseriidx will frequently ascend the sides of the aquarium 

 or float along the under-surfaoe of the water apparently with 



