Bull. U. S. B. F., 1909. 
Plate XXI. 
Organisms constituting the food of mussels. X 900. Diatomacese (modified from Wolle). 
13. Nitzschia sigma var. sigmatella Grunow. X 114. 
14. Melosira sculpta Kiitzing. 
15. Nitzschia sigma Grunow. 
16. Grainmatophora marina Kiitzing. 
17. Rhizoselenia setigera Brighter. X 38. 
18. Pleurosigma balticum W. Smith. 
19. Pleurosigma elongatum W. Smith. 
20. Pleurosigma decorum W. Smith. 
21. Stephanopyxis appendiculata Ehrenberg. 
22. Synedra gallionii Edirenberg. 
23. Hyalodiscus subtilis Bailey. 
24. Pleurosigma angulatum W. Smith. 
25. Coscinodiscus excentricus Ehrenberg. 
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