PLATE XI. 



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



FIG. I. Cosmarium intermedium Delp. 



2. Euastrum elegans (Breb.) Kuetz. 



3. Penium digitus (Ehrenb.) Breb. 



4. Cosmarium latum Breb. 



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



6. Cosmarium sphalerostichum Nordst. 



7. Micrasterias truncata (Corda) Ralfs. 



8. Cosmarium phaseolus Breb. 



9. Cosmarium undulatum Corda. 



n. Micrasterias denticulata (Bre"b.) Ralfs. 



12. Cosmarium pachydermum Lund. 



13. Tetmemorus brebissonii (Menegh.) Ralfs. 



14. Arthrodesmus convergens Ehrenb. 



15. Cosmarium blyttii Wille. 



16. Cosmarium contractum Kirch. 



17. " kilcheliiVfollQ. 



18. Xanthidium armatum (Breb.) Ralfs. 



19. Cosmarium meneghinii braunii (Reinsch.) Hansg. 



20. Pleurotaniopsis debaryi (Archer) Lund. 



21. Cosmarium tumidum Lund. 



22. " ralfsii Bre'b. 



23. Micrasterias kitckeliiVJo\\e. 



24. Euastrum didelta (Turp.) Ralfs. 



25. " elegans (Bre'b.) Kuetz. 



26. " " " Two forms. 



27. Micrasterias oscitans pinnatijida (Kuetz.) Rabenh. 



28. Cosmarium holmiense Lund. 



29. Staurastrum ravenelii Wood, a, front view ; b, end view. 



30. Euastrum elegans, large form. 



31. Micrasterias fimbriata elephanta Wolle. 



[450] (214) 



