No. IO.] FRESH-WATER ALG.E. IO, 



Plectonema Thur. Filaments branched, singly or in 

 pairs, quite irregular, each filament enclosed in a separate 

 sheath ; cell contents deep blue-green. 

 -[P. Wollei Farlow.] 



Symploca Kiitz. Filaments simple or showing mere be- 

 ginnings of branches ; in a more or less distinct sheath, rising 

 from a prostrate base ; glued together into anastomosing or 

 erect, wick-like clusters. 



Lyngbya Ag. (Leibleinia Endlicher; Leptothrix Kiitz., 

 in part ; Spirocoleus Mobius, in part) . Single filaments en- 

 closed in distinct sheaths, either unbranched or with a sug- 

 gestion of branching where the filaments break out of the 

 sheaths. Often forming a membranous stratum. 



L. sp. (?), Fig. 13. 



[L. ochracea (Kiitz.) Thur.] 



Phormidium Kiitz. ( Hyphceothrix Kiitz., in part; Lep- 

 tothrix Kiitz., in part). - A genus between Lyngbya and 

 Oscillatoria. Filaments simple, clothed with a thin, hyaline 

 sheath. Sheaths often become fused, and the trichomes are 

 sometimes so numerous as to form mats on damp ground, 

 stones, etc. The cells are sometimes constricted at the ends, 

 and the apical cell may be attenuated or even thickened. 



[P. Corium (Ag.) Gomont; P. favosum (Bory) Gomont; 

 P. Retzii (Ag.) Gomont; P. uncinatum (Ag.) Gomont.] 



Oscillatoria Vaucher (Oscillaria Bosc). Filaments 

 straight or slightly curved ; only in very young specimens are 

 they coiled ; simple, without a sheath ; mostly bright blue- 

 green, sometimes changing to violet or steel-blue. When in 

 good condition, more or less motile, and involved in a thin 

 mucilage. Found in all sorts of wet places, sometimes even on 

 damp ground and in hot springs. 



O. subtilissima Kiitz., Fig. I. 



0. *ccrugineo-ccorulea Kiitz., Fig. 2. 



O. chalybea Mertens, Fig. 14. 



O. amphibia Ag., Fig. 15. 



O. limosa Ag., Fig. 5. 



0. percursa Kiitz., Fig. 6. 



[O. princeps Vauch. ; O. splendida Grev. ; O. tenuis 

 Ag.] 



