THE NATURAL HISTORY SURVEY. ¥7 
abundant south, but are generally absent north, and the same 
may be said of the Spheria and Pisidia. In the western part 
of the area there are several species which are not found in 
either of the other two regions. 
The writer, from a study of the material at hand, would 
divide the area embraced in the survey into three regions, as 
follows: 
First.—The region lying north of the mouth of the Chicago 
River and east of the Desplaines River, including in its territory 
the north branch of the Chicago River and its tributaries. The 
ground is generally high and free from swamps. The drainage 
is into Lake Michigan by the Chicago River principally, but also 
by several small creeks about Evanston. The district is heavily 
wooded in many places and is especially favorable to the devel- 
opment of land shells; but few fresh-water species are found. 
The following species inhabit this region and, so far as known, 
are not found in the other regions: 
Philomycus oarolinensis. Limnza columella. 
Pupa corticaria. 
Seconp.—The region lying south of the Chicago River and 
east and south of the Desplaines River, including the townships 
of Lake, Hyde Park, Calumet, Worth, Bremen, Thornton, Rich 
and Bloom, and all of the territorial region in Lake County, 
Indiana. The land here is generally low and swampy and con- 
tains the chain of lakes before mentioned. Woodlands are 
scattered about and the region is equally as well suited for land 
as for fresh-water shells. The drainage is into Lake Michigan 
through the small lakes and the Grand and Little Calumet rivers. 
The Illinois and Michigan Canal somewhat mingles the two 
systems of drainages. Unios are particularly abundant. The 
species tabulated below appear to be peculiar to this region. 
Obliquaria reflexa. Polygyra inflecta. 
Quadrula trigona. Polygyra tridentata. 
Quadrula verrucosa. Gastrodonta ligera. 
Quadrula lachrymosa. Gastrodonta demissa. 
Quadrula pustulata. Physa ancillaria. 
Plagiola elegans. Pleurocera subulare. 
Plagiola donaciformis. Campeloma ponderosum. 
Lampsilis multiradiatus. 
Lampsilis gracilis. 
Sphzrium fabale. 
Tuirp.—The region lying west of the Desplaines River, 
including the river, together with the townships of Palos, Or- 
e 
