FRESH-WATER ALG^ OF THE UNITED STATES. 37 



rate fronds are not distinct. The filaments arc very long, mostly closely intricate, 

 very much curved; in some places they are more sparse. Their color is mostly a 

 sort of yellowish ferruginous-green, sometimes they are, decidedly, almost purely 

 ferruginous, more rarely a bright green. This plant agrees pretty well with the 

 descriptions of the European Nostoc comvilnutum, and I believe is the same 

 species; if, however, N. lacustre of Kiitzing is distinct from N. conimiuvfinn, this 

 is also ; but I incline to the opinion that they are all different forms of one plant. 

 Fig. 3, pi. 2, represents a single filameut magnified 800 diameters. 



1¥. commune, Yacch. 



N. terrcstre, tliallo irrcgulariter expanse, difformi, undulato-plicato, trcniulo, intus aquose gela- 

 tinoso, ffitate provecta plerunique excavato, peridermate subcoriaceo firmo, olivaceo, luteo- 

 fuscescente vel luteo-fusco cincto ; trichomatibus flexuoso-curvatis, pallide nenigiiieis, laxe 

 implicatis, ffiqiialibus vel suba;qiialibus, baud raro a basi ad medium usque ecllulis biscriatis 

 compositis; articulis sphaericis vel e mutua pressione subquadrangularibus, laxe conncxis, 

 pas.sim distantibus, puncto central! turbato pra'ditis; celluli.s perdurantibu.s globosis, articu- 

 lorum diametro duplo majoribus, intcrstialibus terminalibusque. 



Dmm.— Cell, vegetat. .00012"— .00016" ; cell, perdurant. .00025"— .00033". 



Syn. — N. commune, Vauch. Rabenhorst, Flora Europ. Algarum, Sect. II. p. 115. 



Bab. — In terrestre, New Jersey. (Austin.) " Rio Bravo. Schott." Harvey. 



Terrestrial ; thallus irregularly expanded, shapeless, undulate-plicate, tremulous, within of the 

 consistence of thin jelly, in advanced age mostly hollow ; periderm subcoriaceous, firm, oliva- 

 ceous, yellowish-fuscous; filaments flexuously curved, pale green, laxly implicate, equal or 

 subequal, not rarely composed of a double series of cells from their base to their middle ; 

 articles spherical or subquadrangular from mutual pressure, loosely connected, here and tliere 

 distant, furnished with a central spot; heterocysts globose, twice as large as the vegetative 

 articles, interstitial and terminal. 



Remarlcs. — The only specimens I have seen of this species are very old ones, 

 which have burst and discharged their central portions. I have consequently pre- 

 ferred to copy the diagnosis of Prof. Rabenhorst. My specimens agree pretty 

 closely with it. The filaments, and also the single cells, are closer together than 

 his words would seem to indicate. My measurements of the heterocysts, as given 

 above, are larger than those of Prof. Rabenhorst. They agree, however, with his 

 text, which his own measurements do not. I am indebted to Prof Austin for 

 specimens of this species, wliich he collected in Northern New Jersey. According 

 to Professor Harvey this plant was collected by Dr. Schott along the Rio Bravo, 

 where it is common on dry flats after rains. 



Subfamily SPERMOSIRE.E. 



Thallus sine peridermate, interdum nullus. Trichoraata sporis instructa. 



Thallus without any periderm, sometimes absent. Filaments furnished with .spores. 



Genus ANAB^NA, Bory. 



Trichoraata moniliformia, evaginata ; sporis sphaericis, anreis vel aureo-fuscis, plerumque singulis, 

 cum cellulis vegetativis vel perdurantibus conjunctis. 



