420 The MoUuscan Family Plaiwrbidae 



PLATE 92 



Shells of Planorbidae 



1,2. Helisoma subcrenatum (Cpr.). Newton, Utah. B3046. 



3. Helisoma suhcrenatum (Cpr.). Stewart River, Yukon Dist., Alaska. U.S.N .M., 



180281. 



4. Helisoma subcrenatum (Cpr.). Cleary, Alaska. Fos.sil pits. U.S.N .M., 381941. 



5. Helisoma subcrenatum (Cpr.). Great Slave Lake. Kennicott Coll., U.S.N.M., 9275. 

 6,7. Helisoma subcrenatum (Cpr.). Wainwright Park, Alberta. B3919. 



8-10. Helisoma subcrenatum (Cpr.). Fort Simpson, Mackenzie District, Canada. Kenni- 

 cott Coll., U.S.N.M., 28378. 



11,12. Helisoma subcrenatum (Cpr.). Creek one mile west of Devon, Montana. Im- 

 matm-e. B3793. 



13-15. Helisoma subcrenatum horni (Tryon). Fort Yukon, Alaska. U.S.N.M., 218908. 



16. Helisoma subcrenatum horni (Tryon). Dall Ri\er, Alaska. Vaiying toward sub- 

 crenatum. U.S.N.M., 180280. 



17-22. Helisoma subcrenatum plexatum (IngersoU). St. Mary Lake, Mineral Co., Colo- 

 rado. Figure 17, lectotype, U.S.N .M., 420210; figs. 18-22, paratypes. U.S.N .M., 

 125130. 



23. Helisoma subcrenatum plexaium (Lig.). Sagnache, Colorado. Lnmature. L^.S.N.M., 

 535328. 



All figures are enlarged about IVj, diameters 



