286 The Molluscan Family Planorbidae 



PLATE 25 



Helisoma pilsbryi (F. C. Baker) 



1-7. Helisoma pilsbryi (F. C. Baker). From Chetek Lake, Barron County, Wisconsin; 

 collected by F. C. Baker. 



1. Penial complex with vergic sac drawn to side of preputium. 



2. Cross section of penial gland. 



3. Pseudobranch and pneumostome. 



4. Outline of genitalia with organs separated. 



5. Penial complex from outside, in normal position. 



6. Penial comjilex of specimen with preimtium pushed upward. 



7. Penial complex showing great length of penial gland duct. 



8-13. Helisoma pilsbryi injracarinatum F. C. Baker. Unless otherwise stated specimens 

 are from Basswood River Rapids, Ontario, Canada; collected by A. R. Cahn. 



8. Penial complex of specimen with large preputium. From Rideau River Rapids, 



Ottawa, Canada; collected by A. LaRocque. 



9. Penial complex with preputium pushed upward, showing length of penial 



gland duct. 



10. Penial complex of immature specimen. From Bamiji Lake, Ontario, Canada; 



collected by Dr. A. R. Cahn. 



11. Pseudobranch and adjacent organs. 



12. Section through prostate and uterus. 



13. Outline of genitalia dissected and organs separated. 



Line near figure indicates 1 mm. in length 



