20 THE CHICAGO ACADEMY OF SCIENCES. 



species may be found in hollows, under leaves, where they have crawled to secure 

 the last drop of moisture. This character of habitat causes the animal to form 

 a varix inside the inner lip, behind which an epiphragm is produced, to protect 

 the mollusk until the area becomes wet again. These varices may be seen to 

 the number of five or six on large shells of capcrata. 



GALBA REFLEXA (Say). Plate LI, figure 2; plate LI I, figure 1. 



This species prefers larger ponds in which vegetation occurs, either reeds 

 or cat-tails, upon the stems of which it hibernates in times of drought, when the 

 water becomes low or entirely evaporates. Occasionally found in muddy bayous, 

 as at Des Moines, Iowa. 



Rcftexa is an inhabitant in many places of transient pools which are well 

 filled with water in the spring, but which wholly or partially dry up in the 

 summer. They, like Galba caperata, form a varix and an epiphragm and hiber- 

 nate during dry seasons, renewing their activities when the pond or pool again 

 becomes moist. Such mollusks as Physa gyrina, Segmentina armigera and 

 Musculium tnmcatum also live in this kind of a habitat. Galba exilis is also 

 characteristic of such a habitat. 



GALBA LANCEATA (Gould). Plate LII, figure 2; plate LIII, figure 1. 



Lanceata usually occupies such habitats as quiet inlets of larger lakes, 

 where there is a quantity of debris, also considerable vegetation. Occasionally 

 it will be found in a marshy portion of the shore of a large lake, as shown in 

 figure 2. Planorbis binneyi is associated with lanceata in figure (plate LII) 

 while Planorbis trivolvis is found with it in the locality figured in 1 on pi-ate LIII. 



GALBA PARVA (Lea). Plate LIV, figures 1 and 2. 



Semi-aquatic species like parva, humilis, humilis modicella, parva sterkii, 

 dalli, etc., freqent the edges of streams (figure 1) and large rivers, especially 

 in those localities where there is a muddy flat. In some places they may be 

 found in debris of various kinds on the margin of large inland lakes (figure 2) 

 or of canals (as the Erie Canal in New York). 



BULIMNEA MEGASOMA (Hald.). Plate LIII, figure 2. 



This fine species lives in very quiet water where the environment is more 

 or less boggy or miry. In Wisconsin this species has been found in miry 

 bayous adjoining the Wisconsin River and tributary streams, near large marshes 

 where the water is from six inches to a foot in depth and the soft, miry mud 

 is from five to six feet in depth. In marshy thoroughfares between the larger 

 lakes, or in small bays where pond lilies are abundant, megasoma may be found 

 near the shore either on the muddy bottom or on drift-wood or floating logs. 

 The bottom of such localities is composed of soft, impalpable mud composed 

 largely of vegetable decomposition. 



LYMN^EA STAGNALIS APPRESSA Say. Plate LV, figure 1. 



Lymnaa stagnalis appressa is typical of quiet bodies of water of a more 

 or less stagnant character. Here it may be found either near the reed-bordered 

 shore or floating in the quiet waters of the bay among Spirogyra or other float- 

 ing vegetation. 



