2 University of Michigan 



The few species of land snails are all common forms of gen- 

 eral distirbution throughout the northern part of lower Michi- 

 gan. With the exception of the two larger species of Polyg>'ra, 

 tliey are also prevalent forms along the shores of the rivers 

 on both sides of the Bay, and, consequently, might easily be 

 waslied out by freshets in times of high water and in this way, 

 perhaps, be carried on floating debris to the islands. It is 

 also possible that the larger species reached the islands in this 

 way. 



List or' Species. 



T. Polygyra albolahris (Say). This species occurs on 

 Charity and Little Charity and shows no special differentia- 

 tion on either. The fourteen mature and perfect spefi- 

 mens collected vary in height from 17 to 20.5 mm., with an 

 average of 18.5, and in diameter from 25 to 28.5 mm., with an 

 average of 26.33. The axial index varies from .65 to .75. 

 witJi an average of .704. A comparison of the average shell 

 of this series with the average shell from the Upper and 

 Lower Peninsula ( AValker Pr. A. N. S. P., 1910, p. 36) may 

 be made as follows : 



LOCAT,ITV. AETITC'DE. DIAMETER. AXIAE INDEX. 



Upper Peninsula 17.02. 25.81. .654. 



Charity Islands 18.51. 26.33. 704. 



IvOwer Peninsula 18.10. 27.10. .677. 



This shows the island shells to be larger in diameter than 

 those from the LTpper Peninsula and smaller than those from 

 the Lower Peninsula, but more elevated than either. 



la. Polygyra albolahris var. dentata (Tryon). A single 

 specimen of this form was collected on Little Charity Island. 



2. Polygyra tiiyroidcs (Say). A few rather thin, pink- 

 tinged examples were collected "under old logs and stumps in 

 the interior of Charity Island." 



3. Polxgvra inonodo:i (Rackett). The typical form, vary- 

 ing from 12 to 14 mm. in diameter, was very abundant on 

 Charity Island. 



4. Pyramidiila dtcrnaia (Say), .\bundant on Charity 



