152 Beautiful Shells. 
amber, and putris means filthy ; but there is nothing 
repulsive about the shell, which, with its variety, 
S. gracilis (slender, is found always near water, 

60. 61-62. 
60. Achatina acicula (the Needle Agate Shell), Miuiller. 
61-62. Succinea putris (the Common Amber Snail), 
Linneus. 63. Physa fontinalis (the Stream Bubble 
Shell), ibid. 64. P. hypnorum (the Slender Bubble Shell), 
ibid. 
either crawling on mud or damp, or attached to 
succulent plants. They are never found, however, 
in the water. Not so Physa fontinalis, as its name 
implies, physa (fuca®), inflated or blown out, and 
fontinalis, residing in springs or fountains. Yet 
the creature is herbivorous, feeding on the leaves, 
especially of Potamogeton, in: lakes and rivers. 
Beneath the water it glides along with moderate, 
uniform motion, produced by the undulations of its 
foot. In the air it advances by jerks, without pro- 
truding its tentacula: and Montagu asserts that it 
will sometimes let itself down gradually by a thread 
affixed to the surface of the water, as the Iimaz 
drops itself from the branch ofa tree. P.hypnorum 
is found in ditches and stagnant pools in many parts 
