662 FRANK COLLINS BAKER 
It would be of great interest to compare other marl faunas of 
Illinois with the one herein described. It is quite probable that 
the new species, as well as the species now showing a more south- 
ward distribution in Pleistocene time, will also occur in other marl 
deposits of the state. 
The collections are in the Museum of Natural History of the 
University of Illinois, and are included in numbers Z10755 to 
Z10803, inclusive. : 
ANNOTATED LIST OF SPECIES 
SPHAERIIDAE _ 
Sphaerium rhomboideum Prime 
A portion of one right valve was the only evidence of the 
presence of this finger-nail clam, which is common, living in the 
northern part of the state. 
Sphaerium occidentale Prime 
One valve, apparently of this species, was observed by Dr. 
Sterki with a lot of Pisidia. It is a common species of the swales 
and small ponds in the northern half of the state. 
Musculium truncatum (Linsley) 
Rather plentiful. A number of specimens differ from the 
typical form in being larger, with narrower, more elevated beaks, 
which are inclined forward. Tvruncatwm is a common species in 
the northern part of Illinois. The beaks of all these Musculia are 
strongly calyculate. 
Musculium cf rosaceum (Prime) 
A single valve is referred doubtfully to this species by Dr. 
Sterki. A single record of this species from the state is given by 
Wolf (1870, p. 27) for Fulton County, but the identification is 
doubtful. There is no authentic record from Illinois as far as 
known to me. 
Pisidium tenuissimum calcareum Sterki 
This fossil Pistdium is the most abundant mollusk in the marl 
bed under discussion, showing considerable variation. It has been 
previously known from the marls of Maine and Michigan, and its 
presence so far south of its hitherto recorded distribution is of great 
interest and indicates clearly a colder climate in early post-glacial 
time. 
