MOLLUSCA. 121 



MOLLUSCA. 



BY H. BURRINGTOX BAKER. 



Introduction. 

 General Discussion. 

 Physiography. 

 Sand Dunes. 



North and Stony Islands. 

 ' Caseville and the Pigeon River. 

 Ru.sh Lake. 

 Geographic Relations. 

 Aquatic Forms. 

 Terrestrial Forms. 

 Habitat Study. 



Aquatic Habitats. 



Habitats of Saginaw Bay. 

 Habitats of the Sand Dune Lakes. 

 Habitats of Rush Lake. 

 Habitats of the Swamps. 

 Habitats of the Pigeon River. 

 Land Habitats. 



Habitats of the Sand Dunes. 

 Habitats of North and Stony Islands. 

 Habitats of the Creek Flats. 

 Habitats of the Clay Soil. 

 List of Habitats. 

 List of Species. 



INTRODUCTION. 



The work that has furnished the basis of this report was done bv the 

 writer while attached to the biological expedition sent out by the Michi- 

 gan Geological and Biological Survey during the summer of 1908. The 

 party made its headquarters on Sand Point, Huron County, but made 

 trips to a number of other places in the vicinity. Thus the writer 

 worked on Sand Point from June 14 to July 12, on Stony and North 

 Islands from July 12 to 20, in the vicinity of Caseville and along the 

 Pigeon River from July 20 to 28, and in the vicinity of Rush Lake (this 

 includes the region between Hat and Oak Points) from July 28 to Au- 

 gust 24. 



In pursuing this work, the writer has become indebted to a number 

 of persons. He wishes to thank all of the members of the party, but 

 especially Dr. Ruthven, for kind assistance in collecting and in locat- 

 ing favorable places to study. He is also under considerable obligation 

 to Mr. C. K. Dodge for the identification of many of the plants of the 

 various habitats. Some of the identifications of the shells were made 



