54 FRANK COLLINS BAKER 



Aplexa hypnorum (Linn.). A few very young specimens, 

 3-4 mm. in length, occurred with the other species in the Carroll 

 County peat deposit. 



Planorhis altissimus Baker. This small Planorhis occurs in 

 sand and silt deposits near Irene, Boone County, in strata believed 

 to be of Sangamon age, and in silt in Whiteside County, of Wabash 

 age. It was most abundant in the Irene deposits. Altissimus 

 is the common small Planorhis of all Pleistocene deposits. As a 

 fossil it has recently been recognized in deposits from Maine, 

 Michigan, Wisconsin, Indiana, Illinois, New Jersey, and Canada 

 (Ontario). It is the species listed as parvus in the writer's Life of 

 the Pleistocene (in most cases, although true parvis does occur in 

 Pleistocene deposits) and in most references to glacial fossils. It 

 was thought to be extinct, but recently Miss Mina L. Winslow, of 

 the Museum of Zoology, University of Michigan, collected a large 

 number of a small Planorhis in Devil's Lake and other water bodies 

 in North Dakota which are apparently the same species. Condi- 

 tions in these lakes are becoming severe, due chiefly to increase of 

 alkalinity, and the species appears to be dying out in the region. 



Planorhis urhanensis Baker. Six specimens of a small Planorhis, 

 first described from deposits in Urbana (Baker, 1918, p. 664; 

 1919, p. 94), occurred in the peat deposit in Carroll County. It 

 does not differ from the Urbana individuals and its presence in a 

 distant part of the state indicates a rather wide distribution. It 

 has probably hitherto been listed under the all-embracing name of 

 parvus. Known only from fossil strata at present. 



Galha palustris (Miiller). Specimens of this protean species 

 were found in deposits near Irene, probably of Sangamon age. 

 These do not differ from living examples of the species. Young 

 individuals, 4 and 6.5 mm. in length, occurred in Wabash deposits 

 in Whiteside County. 



Galha ohrussa (Say) . Broken specimens of this species occurred 

 in post- Wisconsin deposits near Ridott, Stephenson County. 



Galha dalli (Baker). This, the smallest of the lymnaeids, was 

 common in the peat deposit in Carroll County, and in silt deposits 

 in Whiteside County. The specimens are somewhat larger than 

 the types of the Recent individuals from Indiana and there is some 



