348 The Molluscan Family Plauorbidae 



PLATE 56 



Radiilae of Helisoma 

 See remarks on plate 53. Line at bottom of plate indicates 25 microns in length. 



1. Helisoma winsloivi (F. C. Baker). Little Arbor Vitae Lake, Wisconsin. 



70, center tooth; 1-13, lateral teeth; 14, 15, intermediate teeth; 17-19, marginal 

 teeth. 



2. Helisoma trivolvis macrostovium (Whiteaves). Bayfield, Wisconsin. 



53, center tooth; 1-8, lateral teeth; 9-13, intermediate teeth; 14-23, marginal 

 teeth. 



3. Helisoma pilsbryi (F. C. Baker). Chetek Lake, W'isconsin. 



100, center tooth; 1-8, lateral teeth; 10-12, intermediate teeth; 13-23, marginal 

 teeth. 



4. Helisoma pilsbryi infracarinatiim F. C. Baker. Basswood River Rapids, Ontario. 



132, center tooth; 1-9, lateral teeth; 10-14, intermediate teeth; 15-21, marginal 

 teeth. 



5. Helisoma pilsbryi injracarinatnm F. C Baker. Rideau River, Ontario. 



Varying toward pilsbryi. 115, center tooth; 1-13. lateral teeth; 14. 15, interme- 

 diate teeth; 16-29. marginal teeth. 



