118 ILLINOIS BIOLOGICAL MONOGRAPHS [216 



EXPLANATION OF PLATE 



Fig. 29. Amblema undulata. Left valve with channel due to injury. 



Fig. 30. Amblema undulata. Right valve with ridge due to same injury. 



Fig. 31. Strophitus edentulus. Right valve with pearl near posterior end. 



Fig. 32. Strophitus edentulus. Left valve with distomid discoloration. 



Fig. a. Lasmigona costata. Right valve with repaired injur}' near posterior end. 



Fig. 34. Amblema undulata. Spoon River form with rounded shell. 



Fig. 35. Lampsilis venlricosa. Left valve with injured postero-ventral margin. 



Pathologic mussels from Salt Fork. 



