Bull. U. S. B. F., 1930. (Doc. 1097.) 
Figure 5. — Tracings of “foot strips” from fresh-water mussels showing the two types of contraction waves which 
pass over the foot continuously. Upper record from foot of Proptera. (data , the pink heelsplitler; middle 
record from foot of Unio poped. Pope’s purple; lower record from foot of Lampsitis anodontoidcs, the yellow 
sand-shell. Time at bottom of record; single strokes, five seconds each; double strokes, minutes 
