284 The Molluscan Family Planorbidae 



PLATE 24 



Helisoma trivolvis (Say) 



Collected from Oneida Lake, New York, by F. C. Baker, 

 except where otherwise stated. 



L Penial complex. Specimen with portion of preputium containing gland pushed 

 upward. Pool near Green Lake, Wisconsin. 



2. Penial complex in vertical section. Specimen with preputium pushed upward. 



Illinois River, near Peoria, Illinois. 



3. Penial complex. Young specimen with 3Vi> whorls. Devils Lake, Wisconsin. 



4. Section through penial gland showing folds in cup. 



5. Penial complex in immature specimen. Pond near Sturgeon Bay, Wisconsin. 



6. Side view of albumen gland. 



7. Albumen gland from below. 



8. Section through penial gland in specimen in normal, non-breeding condition. 



9. Section through ovotestis near anterior end. 



10. Section through penial complex in region of diaphragm. 



IL External view of penial complex showing duct uncoiled and stretched out, indi- 

 cating great length. 



12. Region of neck showing pseudobranch, pncumostome, rectum, etc. 



13. Section through prostate and uterus near middle of gland. 



14. Penial gland somewhat contracted at cup end. 



15. Genitalia dissected and organs separated. 



Line near figure indicates 1 mm. in length 



