Bull. U. S. B. F., 1919-20. 



Plate V 



Fig. ] . — Rear view of yellow sand-shell in natural position 

 in bottom under water, showing the two siphonal open- 

 ines, the gaping shell, and the apposed mar^jins of the 

 mantle. 



Fig. 2. — Rear view of A nodonta corpulenta showing 

 siphonal openings. Note the very smooth margins of 

 the upper e.^halent opening and the fimbriae or "feel- 

 ers" protecting the lower orinhalent opening. 



Fig. 3. — Tracks of young mussels in crate. 



Change in the conditions of the water had caused them to wander more thau 

 normally. 



