LYMNZIDZ OF NORTH AMERICA. 20 
them. Associated with the Limnea, but much less abundant, are 
Planorbis bicarinatus royalensis Walker, P. campanulatus Say, Lamp- 
silis luteolus (Lam.), Anodonta marginata Say, and Anodonta grandis 
footiana Lea. 
“Opportunity was given to observe the behavior of Limnea sanc- 
te@mari@ in waves of some size near a small circular island half a kilo- 
meter out in the lake. The bottom was gently sloping, and either of - 
solid rock or of large rounded fragments. There were no overhanging 
trees, so the shells were found in uniform abundance in the usual 
depth of water on all sides of the island. At the time the island was 
visited a strong wind was blowing, and the waves were probably nearly 
as high as they ever become on Siskowit Lake. One or two shells 
were seen which had been washed loose and, of course, would be 
unable to reattach themselves until the waves abated. It would be 
expected that in such cases the shells might be crushed or broken or 
the animal killed. That such may happen was evidenced by finding 
a few live shells which had been cracked and then healed, leaving 
an irregular surface. Their occurrence here and elsewhere only upon 
rocks of considrable size shows that they require a firm substratum, 
and where the rocks are free from any coating of slime they can 
certainly endure higher waves. Around the island under discussion 
the rocks were washed perfectly clean. 
“The beach in front of the camp at Siskowit Bay was inhabited 
by large numbers of Physa sayii, Physa sp., Limnea sanctemarie and 
Limnea emarginata, so that more detailed observations of them could 
be made, and a few experiments carried out to show their sensitiveness 
to the depth, or bathytropism, as it has been termed. The beach here 
is of rock with a gentle slope of about one in five, corresponding to 
_the dip, except where blocks have worn off, leaving low vertical walls. 
The wave action here is very light, its force being cut off by a series 
of islands lying between the beach and the main body of Siskowit Bay. 
This was well shown by the conditions on August 2, when there was 
scarcely a ripple inside the islands, although the bay outside was 
covered with whitecaps. The beach is covered with a thin coat of 
slime formed mostly of excrement from the snails. 
“On such a beach snails may live close to the edge of the water, 
but the larger Limnzas still occupy their usual depth of 1.5 to 4.5 
decimeters. About 10 a. m., on August 3, all the shells to a depth of 
about 1 decimeter were gathered from a strip of the beach about 10 
meters long. They were comprised in the following species: Limnea 
sanctemari@, Limnea emarginata, Physa sayii Tapp., and Physa sp. 
