330 THE CHICAGO ACADEMY OF SCIENCES. 



from the left very large and roundly triangular, the side cusps, 

 two on the left and four on the right, sharply triangular; lateral 

 teeth long and narrow, the lower ends rounded, the reflections 

 very wide and low, the first twelve-cuspid and the second six- 

 teen-cuspid (Fig. 117). 



Distribution: Europe and America (the latter introduced), 

 New York, Ohio, Illinois, Michigan, Wisconsin. 



Geological distribution : Pleistocene. 



Habitat: In the larger lakes, on a sandy or muddy bottom, 

 and attached to sticks, stones, and other submerged objects. 



Remarks: This is the largest species of Amnicolidce found 

 in this region. It may be easily distinguished by the size of 

 the last whorl, which more than equals in length that of all 

 the rest. The species was introduced into this country many 

 years ago and is now found from Vermont and New York to 

 Wisconsin. It is particularly abundant in Lake Michigan. 

 While in motion the animal of Bythinia is rather slow, the ten- 

 tacles move about nervously and the rostrum is thrust out to 

 its fullest extent. Thus far it has been collected only in Lake 

 Michigan. 



Recently the Lake View water supply has been seriously 

 threatened by the presence of this snail. The small service 

 pipes became choked and in many private houses a tumbler- 

 ful of these animals was taken from the faucet. Investigation 

 at the Lake View crib showed that the screens were provided 

 -with such a large mesh that the eggs gained access to the main 

 tunnel and there developed, the force of the water drawing 

 them farther and farther into the tunnel until they finally ap- 

 peared in the service pipes. Besides this species, Pleurocera 

 elevatum and Goniobasis livescens were found about the crib, 

 but none on the inside. These were collected in August, 1898. 



Subfamily Hydrobiinae. 



v Shell: Small, elongated or globose, umbilicated or rimate; 

 aperture rounded or ovate; peristome continuous; operculum 

 paucispiral, corneous (Tryon), without internal process. Foot 

 without lateral sinuses. (Stimpson.) 



GENUS AMNICOLA Gould and Haldeman. 



Shell: Small, thin, smooth, globose, umbilicated; spire 

 broadly conic; aperture broadly ovate; outer lip thin; opercu- 

 lum subspiral, corneous. 



