107 



each more or less characteristic. Thirty-six such stations have 

 been closely examined and a study made of their biotic con- 

 tents. The mollusca were exhaustively studied, the associated 

 animals (as birds, reptiles, batrachians, insects, and crustaceans) 

 being also listed. As a study of animal ecology is not complete 

 without a consideration of the associated plants, this important 

 branch of biology has been studied and lists made of the im- 

 portant plant societies. 



A taxonomic study of the mollusca of this region shows the 

 collections secured to embrace two classes, three orders, four- 

 teen families, twenty-three genera, thirty-eight species and 

 varieties, all living within the area three miles long and one mile 

 wide. Of interest in this connection is the discovery that, ap- 

 parently, several species in two families were founded upon age 

 variation. One, Lymnaea reflexa Say, included Lymnaea palu- 

 stris michiganensis Walker (young) and Lymnaea crystalen- 

 sis Baker (immature) ; the other, Physa gyrina Say, included 

 Physa oleacea Tryon (immature.) Twenty terrestrial and eigh- 

 teen fluviatile mollusks were identified. 



The typical molluscan societies and their habitat relations may 

 be summed up as follows : 



Terrestri.\l Species. 



In swamp with Typha or Iris. 

 Succinea retiisa, Siiccinea avara, Agriolimax campestris. 



On low ground subject to overflow. 

 AgrioUmax campestris, Polygyra thyroides, Polygyra fratenia, 

 Pyramidula alternata, Zonitoides arborcus, Vitrea hammonis. 

 On higher ground, raised above overflowk 

 Succinea oralis, Agriolimax campestris, Polygyra albolabris, 

 Philomycus carolinensis. 



On dry ground. 

 Strobilops virgo, Helicodiscus parallelus, Vitrea iudentata, 

 Euconultks fulvus, Bifidaria cont-racta, B. pentodon. 

 Living under "started'' bark, etc. 

 Zonitoides, Vitrea, Strobilops, Helicodiscus, Vertigo, Euconu- 

 lus, Bifidaria, and Carychium. Pyramidida is frequently found 



