LYMN^EIOE OF NORTH AMERICA. 21 



LYMN^A STAGNALIS LILLIANS Baker. Plate LV, figure 2. 



Stagnalis appressa lives in quiet waters but this race, characterized by the 

 shortened up spire and large aperture, is an inhabitant of exposed lake shores 

 where it is frequently subjected to very rough usage by the heavy seas caused 

 by storms and high winds. In Tomahawk Lake, Wisconsin, this race lives on 

 a sandy shore fully exposed to the violence of the waves. In Isle Royale, in 

 Washington Harbor, Lymncea stagnates sanct&maricz is found attached to the 

 rocks, and is not readily removed by the waves. 1 



This race (stagnalis lilliance) has been produced by the change of environ- 

 ment from the quiet waters of protected bays to the rough waters of lakes. A 

 parallel case may be cited in the palustris of Alpena, Michigan, where a change 

 of habitat from quiet, marshy waters to the exposed pools of a lake beach has 

 produced a quite distinct race. 



GALBA EMARGINATA WISCONSINENSIS Baker, also lives on an exposed beach 

 in the Wisconsin lakes, associated with stagnalis lilliana. . 



GALBA WOODRUFFI (Baker). Plate LVI, figure 1. 



At Millers, Indiana, this species is found abundantly on a sandy beach, 

 fully exposed to the violence of the waves. Although no living specimens have 

 been found, it is probable that the species lives not far from shore, as the dead 

 shells are found in abundance all along the southern shore of Lake Michigan. 

 Associated with this Lymnseid are species of Sphcerium, Valvata, Amnicola and 

 Lampsilis. 



GALBA CATASCOPIUM (Say). Plate LVI, figure 2; LVII, figure 1. 



This species is typically an inhabitant of the shore of quiet rivers or lakes 

 where it may browse among the algae along the shore. In the Genesee River and 

 in the Erie Canal (figure 2) at Rochester, N. Y., this species may be found 

 by countless thousands along the quiet shores of these streams. Some forms, 

 by change of habit to the exposed shore of a large lake or bay, as at Pine 

 Lake, near Charlevoix, Michigan, have developed a smaller, more solid shell 

 than those individuals inhabiting the quiet areas mentioned above. Along the 

 shore of Lake Ontario, where pools of water have collected behind breakwaters 

 (due to rough water), this species lives in large numbers on the mud flats in 

 shallow water (pi. LVII, fig. 1). In the Delaware River, catascopium lives 

 between tides and is subject to all the influences of the littoral marine species. 



GALBA PALUSTRIS (Muller). Pla-te LVII, figure 2. 



Palustris is characteristic of stagnant ponds and swampy pools, where 

 there is a quantity of vegetation, both living and dead. The edge of a Typha 

 latifolia plant society is .almost always a favorite resort of this species (pi. LV, 

 fig. 1). 



PSEUDOSUCCINEA COLUMELLA (Say). Plate LVIII, figure 1. 



This fragile Lymnaea lives in a quiet, stagnant habitat, usually among cat- 

 tails (Typha). The surface of the water is usually covered with pond scum 

 (Spirogyra) or other floating vegetation. A pond filled more or less with lily- 

 pads also affords a typical habitat for this -species (pi. LIII, fig. 2). 



When the habitat is a rapidly flowing stream, the shell tends to 

 become solid and to produce a large aperture to enable it to withstand 



*c. f. Adams, Ecol. Surv. Mich., p. 97. 



