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 S. MORSE. 

Awoxe the most common of our fresh-water mollusks are 
the air-breathing water snails. Muddy lakes, ponds, streams 
and marshes, being their favorite abodes, and even ditches 
sometimes swarming with them. It would be difficult to 
find a body of fresh-water that did not contain certain repre- 
sentatives of this class. 
Their shells are quite uniform in texture and color, con- 
taining but little lime, and for this reason are quite light, 
and even in some species slightly elastic. They are quite 
hardy in confinement, and a few 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 surface 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 by 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, and then a funnel-like process is opened in such a 
way that 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 laid upon 
me glass walls of an aquarium, or the sides of a glass dish, 

TNCS 


