34 JEAN DAWSON 



outside the small pool of water. In one small area where the 

 ground was damp, a number of Physa elliptica Lea and Plan- 

 orbis parvus Say were found lying on the ground. It is a notable 

 fact that when they had the aperture down they were living in 

 more cases then when the aperture was turned up. 



The border of the swamp was very dry. No snails were found 

 living except three specimens of Lyninaea palustris which were 

 found sticking, aperture down in the clay. 



Swamp A ^ This swamp is cleared and is surrounded by 

 open pasture lands. The swamp basin is shallow, very. level 

 and has no standing water, although the ground in many places 

 is moist. It has no water weeds except Alisma plantago, also 

 fotmd in the pond near the campus. 



Erosion on some of the hillsides had taken place quite rapidly ; 

 so that patches of clay and sand several feet square cover 

 the peat on the border of the swamp. While there were many 

 dead shells of Lymnaea palustris (the only mollusk in the swamp 

 except Sphaerumi, strewn over the surface) , there were places moist 

 enough, both on the sand and clay to support snail life. Many 

 Lymnaea were found living on the clay washed from the hills, 

 while few were found on the sand. A very remarkable instance 

 of desiccation was found upon a large boulder which lay on 

 one side of the swamp. About twenty snails were left upon the 

 top of this stone when the water receded. One of them was 

 found living, aperture up. Upon examination the snail was 

 seen to have formed a complete mucous epiphragm over the 

 aperture. This seemed remarkable as the snail lay fully exposed 

 to the sun on the top of the stone which was fully a foot above 

 the level of the bottom of the swamp. 



Group B is very much the same as Group A. except that 

 the ground is wholly dried up. 



Group B — Swamp B\ This swamp is surrounded by gently 

 sloping hills covered with grass. All the trees have been felled 

 and many of the logs are still lying where they have fallen. The 

 ground contains moisture (although no standing water is 

 seen) and is covered with an abundant growth of Hypnum six 

 to eight inches in thickness, which, when the water was lowered, 

 settled upon the logs and bed as a heavy blanket. Some of this 

 moss was damp and one specimen of Lymnaea palustris was found 

 alive upon it although hundreds of dead shells lay under the 



