
MOLLUSCS, VERMES AND HYDROZOA 

leaves by clean cuts across the blades, others by devouring the edges. If 
the aquarium is not covered they leave the water and crawling on the 
glass and over the edges dry out and die. One was found twenty feet 
from the nearest aquarium. 
PLanorsis. This numerously represented genus has the spiral shell 
flattened so that the view from above, below and on each side 1s different. 
The species vary in size, the largest being one and a half inch in diameter 
and the smallest less than g inch. It is the best native easily procured 
snail for the aquarium, preferring alge to any other food, and if not over- 
stocked is harmless to aquatic plants and is a good scavenger. 
P. bicarinatus, Fig. 168, has a brownish-grey shell never over 1% inch 
in diameter, showing pale grey lines in the suture, with more than three 
complete whorls, angulated on 
each side with a slightly keeled 
periphery. The spire is on the 
left side and is depressed as deeply 
as on the other side. The body 
is a dusky or blackish-brown and 
the tentacles a yellowish-brown, 

generally of varying lengths. It 
inhabits quiet waters from New 
England to Georgia and west- 
ward to Tennessee, and will hi- 

bernate in cold water. The eggs 
are deposited from March to 
July in small irregular yellow masses and hatch in 15 to 25 days, depend- 
ent upon the temperature. 
P. campanulatus, Fig 169, has a yellowish 34 inch in diameter compact 
shell, consisting of four slowly enlarging flattened whorls, distinctly marked 
FIG. 168. Planorbis bicarinatus, four views. Enlarged. 

four views. Enlarged. 
