204 LAND AND FRESH-WATER MOLLUSKS. 
It is a very active creature, and ascends at 
will to the surface in a direct line, or returns to 
the bottom, or holds itself suspended in the 
water, with facility; its habits may be well ob- 
served in the aquarium. The above-mentioned 
movements of this snail are, according to Mr. J. 
Jones, effected in the following manner: “ The 
edges of the foot are brought closely together, 
converting that member into a tube, from which 
the column of water therein enclosed is expelled 
with considerable force, either upwards or down- 
wards, as the animal may be disposed to ascend 
or descend, being, in fact, a modification of the 
mode of locomotion adopted by the cuttle-fish, 
which effects its rapid movements by ejecting 
water through a funnel.” The Pisidiums, the 
glass-bubble shell, and some of- the pond- 
snails, as previously stated, exhibit the same 
powers; and it is the accepted explanation, that 
the snail does so by means of glutinous threads. 
Mr. W. Nelson charges the present species with 
cannibalism; he writes, * * * * “on looking 
again, three or four days after, I found some more 
shells empty, but this time caught five or six of 
the real delinquents busily feeding on the dead 
body of one of their comrades, and one of the 
empty shells had a rather large hole in the whorl 
next to the body-whorl.” 
