LYMNZIDZ OF NORTH AMERICA. 39 
cure free air from bubbles which have become entangled in some ob- 
jects below the surface. Pauly was able to observe a number of indi- 
viduals actually secure the air from these bubbles, but Walter was not 
able to verify this observation during his studies on the behavior of the 
pond snails. (Walter, p. 20.) The author has frequently seen fresh- 
water pulmonates in the vicinity of air bubbles and there is no reason 
to doubt the accuracy of Pauly’s observations. 
Pauly’s third class of abnormal breathing, that of snails artificially 
deprived of air, bears upon a very interesting subject, that of the 
ability of Lymnza to return to the ancestral habit of extracting the 
oxygen from the water, as observed in those snails living in very deep 
lakes and also in young Lymnzas. The observations of Moquin-Tan- 
don, Saint-Simon, Pauly, Walter, etc., all tend to show that Lymnza 
is unable to suddenly adapt itself to the water breathing habit. In some 
of the experiments Lymnea stagnalis and Lymnea elongata were used, 
Lymnea stagnalis surviving from 22 to 91 days, but finally succumb- 
ing. It is interesting to note that the deep water forms easily and 
readily adapt themselves to the surface-visiting habits of their shal- 
low-water relatives. 
e. ZESTIVATION. 
During seasons of drought when the ponds and streams dry up, 
the Lymnzas bury themselves in the mud to the depth of several inches, 
form a rib or varix within the outer lip and cover the aperture with an 
epiphragm like the hibernating helices. This is especially true of those 
species or races which inhabit intermittent streams or summer-dry 
ponds. Cooke’ records Lymnea peregra as burying itself to the depth 
of three inches, “when surprised by a sudden fall of water in the ditch 
on Coe Fen, behind Peterhouse, Cambridge.” Galba truncatula has 
been found buried in hard dry mud to the depth of 18 inches.? 
Lymnea is able to survive for considerable periods when deprived 
of water. Many of the smaller species (parva, humilis, obrussa) will 
voluntarily leave the water and remain for a considerable time on 
stones, sticks and other material on the land. Several of these species 
are sometimes found quite a distance from water. The European 
Galba truncatula has been reported by Jeffery* as living far from 
water. The large species are not known to possess this habit, although 
they will live for a long time without water, if placed in wet moss or 
cotton. Wiedersheim® has recorded the instance of Radix auricularia 
1Mollusca, p. 27. 
2Op. cit., p. 41. 
*Zoologischer Anzeiger, II, p. 573, 1879. 
‘Journs Conch.,, Tl, sp. 305, 1882. 
