410 The MoUuscan Family Plmiorhidae 



PLATE 87 



Shells of Planorbidae 



1-4. HeUsoma trivoJvis fallax (Haldeman). Milton Mills, Milton, Massachusetts. U.I., 



Z41108. 

 5-7. HcUsotna trivolvis fallax (Haldeman). Green Lodge, Xeponset. Massachusetts. 



B904. 

 8,9. Hclisoma trivolvis fallax (Haldeman). Fresh Pond, Cambridge, Massachusetts. 



U.S.N.M., 33657L 

 10. Helisomn trivolvis fallax (Haldeman). Port Elizabeth, Maine. U.S.X.M., 26449. 

 11-15. HeUsoma trivolvis marshnlli F. C. Baker. Washington, D.C. 13, holotype; 



11-12, paratypes; 14-15, immature. U.S.N .M., 124989. 

 16. HeUsoma trivolvis marshalli F. C. Baker. New Jersey. LT.S.N.M., 504153. 

 17-20. HeUsoma trivolvis holstonense F. C. Baker. Holston River, Smith Co., Virginia. 



17, holotype; 18-20, paratypes. U.I., Z41443. 



21. HeUsoma trivolvis lentum (Say). New Orleans, Louisiana. Immature. Aquarium 



specimen. B3918. 



22. Hclisoma trivolvis holstonense F. C. Baker. Holston River, Virginia. Immature. 



U.I., Z41444. 

 23,24. HeUsoma trivolvis holstonense F. C. Baker. Holston River, Virginia. Variation 

 in color. U.I., Z41444. 



All figiu'es are enlarged about two diameters 



