Th: ECOLOGY OF THE LYMNAZAS. 
a. GENERAL ENVIRONMENTAL CONDITIONS. 
The Lymnzeas inhabit all varieties of bodies of water, from the 
small transient pool to the great lakes. While the family as a whole 
is thus widely distributed, many of the species are quite restricted in 
their habitat. Some species (stagnalis appressa, for example) live 
in marshy, reed-bordered iakes and ponds, preferring open patches 
of water near the shore in early spring and venturing out into the 
larger body of water in the fall. Another group of species represented 
by palustris prefers stagnant ponds where there is considerable decay- 
ing vegetation. They may be found crawling over the bottom of the 
pond or pool, on the vegetation or on any other submerged object. 
Some of the species, like caperata, live in small running streams, in 
stagnant overflows of creeks, or in small pools which dry up in periods 
of drought. The small species, like parva and humilis modicella, live 
on the margins of streams, ponds and creeks, on the mud bordering 
the shore or on sticks, stones and various kinds of débris. These 
species are seldom found in the water, unless recently submerged by 
a rise of the water, their natural habitat seeming to be just above 
high-water mark. When kept in captivity they invariably crawl out 
of the aquarium and may be found on tables, chairs or even the floor. 
A few Lymnezas, like apicina and emarginata, prefer a rocky habitat, 
either in running water or where there is a decided wave action as 
on the beach of Lake Superior in Ontonagon County, Michigan, and 
on the sandy shores of the larger inland lakes, like Tomahawk Lake, 
Wisconsin. So important has it become that exact data should be 
secured concerning the environmental relations of animal groups that 
it has been thought necessary to illustrate a few of the more typical 
and noteworthy habitats of a few species of Lymnza. As the central 
United States is the metropolis of this family in North America, the 
illustrations and examples are mostly taken from this region. 
GALBA CAPERATA (Say). Plates L; LI, figure 1. 
This species, in company with Aplera hypnorum and Spherium occidentale, 
lives in small streams, overflowed portions of small rivers and creeks, and in 
small transient pools in the woods. (Plate LI.) In the summer and fall these 
1It is not to be supposed that the different species occupy only stations 
like those pictured. They will be found in any locality furnishing a more or 
less similar set of conditions. 
