648 OUR FRESH-WATER SHELLS. 



usual range does not extend much to the eastward of the 

 Mississippi River, and of two not usually found east of the 

 Rocky Mountains, and of others that rarely occur north of 

 Florida, shows the possibility of a species becoming widely 

 diffused over districts favorable to its existence by occasional 

 migrations. 



OUR COMMON FRESH-WATER SHELLS. 



BY EDWARD 8. MORSE. 



AMOXQ\the most common of our fresh-water mollusks are 

 the air-breaking water snails. Muddy lakes, ponds, streams 

 and marshes^sbeing their favorite abodes, and 7 even ditches 

 sometimes swarming with them. It would be difficult to 

 find a body of fre&U-water that did not contain certain repre- 

 sentatives of this claXs. 



Their shells are quite uniform in texture and color, con- 

 taining but little lime, ai^d for this reason are quite light, 

 and even in some speciesNslightly elastic. They are quite 

 hardy in confinement, and a fttw specimens secured in early 

 spring time will afford many pleasant hours of amusement 

 to those interested in watching their habits. They have to 

 come often to the surfa'ce of the water to breathe, and it is 

 curious to watch them during this operation. The snail with 

 its broad disk slowly sweeping along the glass, feeding at 

 the same time l;>y lapping up whatever particles of food it 

 may meet with. As it nears the surface the shell is inclined 

 in such a way that the aperture is brought almost out of 

 water, an$ then a funnel-like process is opened in such a 

 way thatf the air enters the respiratory cavity, while the 

 water/seems to be repelled by the edge of the funnel. 



During the spring time the eggs are laid and attached 

 to some substance by a transparent mucous. If laicl upon 

 the glass walls of an aquarium, or the sides of a glass dish, v 



