PLATE XI. 



[Proc. Wash Acad. Sci., Vol. Ill, PI. XLIV.] 



FIG. i. Cosmarium intermedium Delp. 



2. Euastrum clegans (Breb.) Kuetz. 



3. Pen in m digitiis (Ehrenb.) Breb. 



4. Cosmarium la turn Breb. 



5. Staurastrum dejeciiim Breb. a, b and c. 



6. Cosmarium sphalerostichum Nordst. 



7. Micrasterias truncata (Corda) Ralfs. 



8. Cosmarium phaseolus Breb. 



9. Cosmarium undulatum Corda. 



11. Micrasterias denticulata (Breb.) Ralfs. 



12. Cosmarium pachydermum Lund. 



13. Tctmemorns brebissonii (Menegh.) Ralfs. 



14. Artfirodesmus convergent Ehrenb. 



15. Cosmarium &fyttii'Wille. 



16. Cosmarium contractual Kirch. 



17. " kitchelii Wolle. 



18. Xanthidium armatum (Breb.) Ralfs. 



19. Cosmarium mcncghinii b raunii (Reinsch.) Hansg. 



20. Pleurotceniopsis dcbaryi (Archer) Lund. 



21. Cosmarium tumidum Lund. 



22. " ralfsit"Br6b. 



23. Micrasterias kitchelii Wolle. 



24. Euastrum didclta (Turp.) Ralfs. 



25. " elegans (Breb.) Kuetz. 



26. " " " Two forms. 



27. Micrasterias oscitans pinnatifida (Kuetz.) Rabenh. 



28. Cosmarium holmiensc Lund. 



29. Staurastriim ravenclii Wood, a, front view ; b, end view. 



30. Euastrum elegant, large form. 



31. Micrasterias fimbriata elephanta Wolle. 



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