THE NATURAL HISTORY SURVEY. 
The Mollusca, the title of Bulletin Number III. of The 
Natural History Survey, will be issued in two parts. The sub- 
ject of the present report is the Pelecypoda, and a later 
publication will treat of the Gastropoda. 
The work has been prepared by Mr. Frank Collins Baker, 
Curator of The Chicago Academy of Sciences, who has not only 
illustrated all species described, by half tones or zinc etchings 
made from original photographs and drawings, but has also 
placed in the collection of the Academy a large number of 
specimens showing the development of and variations in each 
species found in the area covered by the Survey. 
The territory embraced by the publications of the Survey 
includes Cook and DuPage Counties and the nine north town- 
ships of Will County in Illinois, and a portion of Lake County, 
Indiana. This area gives a surface of about forty-eight or fifty 
miles square, or a land surface of nearly 1,800 square miles. 
All species have been described and keys prepared, 
in order that the work may be used as a text-book for the local 
forms of the Mollusca, thus making the subject available to many 
students who are deterred from pursuing the study because of 
the high price and rarity of most of the text-books on this 
subject. 
For the reason that Part II. will soon be issued, it has been 
thought best to withhold the bibliography, glossary and index 
until the second part is published, and to then make them com- 
plete for both parts. It was found that in making the plates, 
illustrations of three species of Pisidium had been included 
with a number of gastropods, hence this plate has been reserved 
for Part II., and the references to it have been made accordingly. 
The Board of Managers of the Survey takes pleasure in 
acknowledging its obligation to Mr. Charles T. Simpson, of the 
Smithsonian Institution, who not only examined the manu- 
script of the bulletin, making many valuable suggestions, but 
reviewed the family Unionidae and added original matter of his 
own which is here published for the first time. The board also 
wishes to express its appreciation of the valuable suggestions 
