16 Trans. Acad. JSci. of St. Louis. 



lateral to the right of the central tooth had a bifid outer cusp. 



This was observed in all the first laterals in this membrane. 



Distribution: North America, Europe, 



Asia; circumpolar. Alaska (Randolph). 



Geological Distribution: Pleistocene; 



Loess. 



Habitat: Found in small streams and 

 rivers, ponds and lakes, attached to float- 

 ing sticks and submerged water plants. 

 Remarks : This is a very common and 

 also a very variable species, as the list of 

 Fig. 9. First lateral of synonyms which heads the description 

 L.palmtris,y^ithum will attest. It is always a wide, more 

 outer cusp. - .- . i i 



or less fusiform species, with the aper- 

 ture and spire equal, or the latter a trifle longer, but never 

 twice as long, as in reflexa. The malleation is usually, 

 though not always, present. There seem to be no geographic 

 races to this form, as all varieties may be found in a single 

 small pool, as is the case near Bowmanville. The lip may 

 be thin or thickened, without regard to size. Some forms 

 arc'ornamented by numerous fine, incremental lines, much as 

 in some land shells. 



The food of the Limnaeids is supposed to be exclusively 

 vegetable, but from some recent observations and from late 

 notes of other naturalists it would seem that the group is 

 carnivorous as well as scavengiferous. The writer has noted 

 this species feeding upon dead carcasses (dogs, cats, etc.) 

 and Dr. Sterki (The Nautilus. 5 : 94. 1891) has seen it in the 

 act of eating a living leach. The species is found in almost 

 all parts of the area and in some localities is the predominat- 

 ing form. 



The animal of palustris is very rapid in movement. It 

 crawls out of the water and will remain in this position for a 

 long time. When crawling, the shell is frequently moved 

 rapidly from side to side, and is carried at all conceivable 

 angles. It is a very rapid feeder and will soon clear up the 

 sides of an aquarium. Like other species of the genus, palus- 

 tris has the habit of rising very suddenly from the bottom to 

 the top of the water where it will then float shell downward. 



