Buy. U.S. B. F., 1917-18. PLATE XXI. 
Upper pair: Kidney-shell, Pivchobranchus phaseolus (Hildreth), from Obey River, Ky. (See p. 33.) 
Lower pair: Rock pocketbook, Arcidens confragosus (Say), {rom Mississippi River. (See p. 34.) 
