32 
Plate III 
Figures 1—8. Helisoma trivolvis (Say). Figures 1-4, Braddocks bay, near Rochester, 
NA„ University Illinois, Z29789; figure 5, Oneida lake. N.Y.. showing flaring aper- 
ture figured by Binney; figure 6. same locality but aperture not flaring, Baker coll., 
905; figures 7-8, Ottawa river, Ontario, Baker coll., 8005. 
Figures 9-14 ; Helisoma plexatum (Ingersoll). Figure® 9-10, Boulder, Col.. University 
Illinois, Z32500; figures 11-12. 2 miles above Harrieanaw river, Hannah bay, Out., 
collected by Spread borough, Nat. Mus., Canada, 3149; figures 13-14, Black Bear 
island, lake Winnipeg. Man., Dowling and Lambe coll., Nat. Mus., Canada, 2156. 
Figures 15 16. Helisoma suberenatum (Cpr.). Little lake, near west end Great Slave 
lake, Mackenzie river, Nat. Mus., Canada, 3148. 
Figures 17. 20. Helisoma trivolvis (Say). Transition form. Pond near Presqu’ile, lake 
Huron. University Illinois, Z23749. 
Figures 18. 21. Helisoma trivolvis maerostoinum (Whiteaves). Pond near Bayfield, 
Bayfield county, Wis. University Illinois, Z 13677a. 
Figures 19. 22. Helisoma trivolvis macrostomum (Whiteaves) . Bamaji lake. Out. Univer- 
sity Illinois, Z30857a. 
Figures enlarged li diameters. 
