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. 



Planorbis. This numerously represented genus has the spiral shell 

 flattened so that the view from above, below and on each side is different. 

 The species vary in size, the largest being one and a half inch in diameter 

 and the smallest less than ^ inch. It is the best native easily procured 

 snail for the aquarium, preferring algas to any other food, and if not over- 

 stocked is harmless to aquatic plants and is a good scavenger. 



P. iicarinaf us. Fig. 1 68, has a brownish-grey shell never over ^ 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 I | 



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 fig. 1 68. PWri«w<:«r,w«., four views. Enlarged. 



July in small irregular yellow masses and hatch in 15 to 25 days, depend- 

 ent upon the tefnperature. 



P. campanulatus. Fig 169, has a yellowish ^ inch in diameter compact 

 shell, consisting of four slowly enlarging flattened whorls, distinctly marked 



FIG. 169. Planorbis campanulatus^ four views. Enlarged. 



