1809.] ■^^-' [Wood. 



latis et ad genicula eoiitractis ; cytiodermate dilute caeruleo-viride, 

 plerunique copiose granulato, saepe interrupto ; cellulis perdurantibus 

 cylindricis, saepe elongatis, saturate brunneis, spai'sissimis ; vaginisfirmis, 

 achrois, in tricliomata niatura modice crassis. 



L. with the filaments closely interwoven into a blackish green mat ; 

 filaments variously curved, simj)le, mostly inarticulate, sometimes shortly 

 articulate with the joints contracted ; endochrome light bluish green, 

 mostly very granulate, often interrupted ; heterocysts cylindrical, often 

 elongate, deep brown, very few; sheaths firm, transparent, in old fila- 

 ments moderately thick. 



Diam. ttoo"- 



Hab. In flumine Schuylkill prope Philadelphia. 



FAM. NOSTOCHACEAE. 



GEN. NOSTOC. 



K. CALCICOLA. Ag. 



Hab. In rupibus prope Catoosa Springs, Georgia. — Prof. Ravenel. 



Remarks. — The heterocysts in the American plant are both intermixed 

 and terminal, otherwise the description of the European form is well 

 answered. The region of country in which the specimen was collected 

 is a limestone one. I am unable to say more positively whether the rocks 

 on which it was growing were limestone or not. 



GEN. SPHAEROZYGA. 



s. POLYSPERJiA. Bahenliorst. 

 In stagnis pi'ope Camden, New Jersey. 



S. STJBRIGIDA. S'p. NoV. 



S. natans ; trichomatibus singulis, rectis aut subrectis, minimis, dilute 

 viridibus ; articulis cylindricis aut subglobosis, distinctis ; sporis cylin- 

 dricis, in medio gradatim nonnihil constrictis, singulis aut duplicis, sine 

 cellulis perdurantibus inter se ; cellulis perdurantibus brevecylindricis, 

 singulis, distinctis. 



S. Floating ; filaments single, straight or straightish, very small light 

 green ; articles cylindrical or subglobose, distinct ; spores single or 

 double, in the middle gradually a little constricted, not having a hetero- 

 cyst between them ; heterocysts shortly cylindrical, single, distinct. 



Diam. cell. veg. trans. ^ 0^00"=. 00016 ; spor. transv. ^oo"-f5o(r""" 

 .00023"-.00022" ; long. ^1^^"=. 00066" ; cell. perd. transv. 4 0^^^"=. 00022. 



Hab. In stagnis prope Philadelphia. 



GEK. CYLIXDROSPERMUM. 



c. FLEXUGSUM. {Ag.) Raoenh. 

 Hab. In humo irrorato prope Philadelphia. 



