to mark types of localities. These appear at the head of each 

 column and are explained as follows : 



I. — Terrestrial species from the forest and forest border 

 areas. 



II- — Aquatic, mostly pulmonate forms, from shallow waters 

 and swamp borders. Here are also included several 

 species, marked by asterisks, which are only semi- 

 aquatic, living on wet borders, etc. They are sometimes 

 truly terrestrial. 



III. — Aquatic species from the deeper waters of the lakes and 



larger ponds. 



IV. — Fluviatile forms from the Little Sioux river. 



V. — Fluviatile forms from the Des Moines river at Esther- 



VI. — Species from the lacustrine deposits south of Miller's 

 Bay and at the northern extremity of Upper Gar lake. 



2. — The numbers in the columns indicate the abundance and 

 extent of distribution as follows : 1 marks species which are very 

 common and widely distributed ; 2 indicates rather common spe- 

 cies, less abundant but generally distributed ; 3 denotes that the 

 species is quite widely distributed, but is nowhere common; 4 

 marks rare species ; and 5 designates species now extinct in this 

 region. Of the latter one species, Lymnwa megasoma, has ex- 

 isted in the region within a half century, as specimens were col- 

 lected by the White Geological Survey. 



ville. 



TABLE OF MOLLUSCA 



I I in 



III 



IV 



V I VI 



Polygyra profunda (Say) Pils. 

 Polygyra fraterna (Say) Pils. 



4 

 3 

 4 

 2 



Polygyra monodon (Eack.) Pils. 

 Bifidaria contracta (Say) Sterk. 

 Bifidaria armifera (Say) Sterk. 

 Bifidaria corticaria (Say) Sterk. 

 Bifidaria pentodon (Say) Sterk. 

 Bifidaria holzingeri (Sterk.) 



2 

 4 

 4 

 3 

 3 

 3 

 2 



9 



2 



Bifidaria curvidens (Gld.) Sterk. 

 Pupoides marginatus (Say) Pils. & Van. 



Vertigo ovata Say 



Vertigo milium (Gld.) Binn. 



Vertigo tridentata Wolf. 



Cochlicopa lubrica (Muell.) Per. 



72 



