258 EXPLANATION OF THE PLATES. 



Fig. 6. Closterium Leibleinii, Ktz., magnified 260 diameters. 



Fig. 7. Tetmemorus giganteus, Wood., magnified 260 diameters. 



Fig. 8. Tetmemorus granulatus (Breb.), magnified 450 diameters. 



Fig. 9. Pleuroteenium Trabecula (Ehrb.), magnified 160 diameters. 



Fig. 10. Spirotsenia bryophila (Breb.). 



Fig. 11. Spirotaenia condensata, Breb. 



Fig. 12. JSyalotheca dissiliens, Breb. 



Fig. 13. Didymoprium Orevillii, Ktz. 



Fig. 13 a. End view. 



Fig. 14. Cosmarium Botrytis (Bory.), magnified 460 diameters. 



Fig. 15. Cosmarium Cucumis, Corda. 



Fig. 15 d. A frond in which the neck or isthmus has begun to elongate previous to division. 

 Fig. 15 b. An abnormal frond which has attempted division, but in which the inner senucells of 

 the new frond have failed to form perfectly and to separate. 

 Fig. 16. Euastrum multilobatum, Wood ; front view. 

 Fig. 17. Micrasterias Americana (Ehrb.). 



Fig. 18. Cosmarium Meneghenii, Breb., magnified 750 diameters. The sinus should be very 

 narrow but distinct, instead of being absent as in the figure. 



Fig. 19. Spirogyra Weberi, Ktz., portions of conjugating filaments, magnified 260 diameters. 



Fig. 19 a. A portion of a sterile filament, magnified 160 diameters. 



Fig. 19 6. Conjugating cells with nearly mature spores, magnified 260 diameters. 



Fig. 20. Closterium juncidum, Ralfs., magnified 260 diameters. 



Fig. 21. Cosmarium margaritiferum (Turp.), magnified 460 diameters. 



PLATE XIII. 



Fig. 1. Front view of Euastrum Ealfsii, Rabenh., magnified 450 diameters. 



Fig. 2. Front of Euastrum elegans, Breb., enlarged 750 diameters. 



Fig. 3. Front view of Euastrum binale (Turp.), magnified 750 diameters. 



Fig. 4. Front view of Micrastejria dispulata, Wood, drawn from a Philadelphia specimen. 



Fig. 4 a. The same after a figure drawn by Dr. Jos. Leidy, from a Newport specimen. 



Fig. 5. Micrasterias furcata, Agardh., front view, magnified 260 diameters. 



Fig. 6. Front view of Micrasterias denticulata, Breb., magnified 260 diameters. 



Fig. 7. Micrasteria Jenneri, Ralfs. Front view. 



Fig. 8. Staurastrum orbiculare (Ehrb.). Front view. 



Fig. 9. Staurastrum dejectum, Breb. Front view, magnified 750 diameters. 



Fig. 10. Staurastrum punctulatum, Breb. Front view. 

 Fig. 10 a. View from the apex. 



Fig. 11. Front view of Staurastrum Lewisii, Wood, magnified 750 diameters. 

 Fig. 12. Front view of Staurastrum polytrichum, Perty. 



Fig. 13 a. Front view of Staurastrum munitum, Wood. 

 Fig. 13 b. End view of the same. 



Fig. 14. Cosmarium pyramidalum, Brebisson. Front view. 



