16 THE. CHICAGO ACADEMY OF SCIENCES. 
woods there is a small stream in which a great diversity of 
Physez may be found. 
CaLtuMET River.—This river runs through Lake County, 
Indiana, and Thornton and Hyde Park townships, Cook County, 
Illinois, in a north and westerly direction and empties into 
Lake Michigan. The only portion in which collections have 
been made is that part lying in Hyde Park Township. It is 
from eleven to fifteen miles from Chicago. The banks are 
muddy and at the present time are denuded of woodlands. The 
water is of considerable depth, but along the shores there are 
shallows in which mollusks are numerous. 
Other good points which may be mentioned are Avondale, 
Edgebrook, Blue Island, Riverdale, the south branch of the 
Chicago River, Riverside, Dunning, Lemont, Hickory Creek, 
Rock Run, the Illinois and Michigan Canal, Naperville, Lock- 
port, Willow Springs, Romeo, Salt Creek and Thorn Creek. 
In several parts of the area under discussion the natural 
drainage has been much affected by artificial canals; in the 
southern region the old canal feeder connects the Desplaines 
River with Stony Creek, which causes the waters of the Little 
Calumet River to mingle with those of the Desplaines River. In 
the middle of the area the waters of the Illinois and Michigan 
Canal and the south branch of the Chicago River mingle with 
the waters of the Desplaines River and Lake Michigan. These 
facts probably account to some extent for the similarity of the 
Mississippi Valley and Great Lake faune. 
IV. GEOGRAPHICAL DISTRIBUTION. 
The geographical distribution of the species within the 
area is interesting. The present lakes and ponds of large size 
are the relics of the glacial period and were once included in 
the area of Lake Michigan, or Lake Chicago, as it is called 
geologically (Fig. 1). The receding of the lake has left a 
peculiar distribution of the molluscan fauna, especially the land 
snails. Thus we find that there are certain species found in the 
northern part of the area which are not found in the southern 
part, and vice versa. Polygyra albolabris, P. tridentata, Pyram- 
idula solitaria and Pupa fallax are not found in the northern 
region, but are abundant in the southern region. So also with 
Planorbis campanulatus and P. bicarinatus which are abundant 
south, but so far as known, absent north. The Unios are all 
