32 FRESn-WATER ALGJ3 OF THE UNITED STATES. 



the only differences between them and the European plant are that they arc not so 

 large, and do not agree in color, many of them being browner; but these are certainly 

 insufficient grounds for separating them. Prof. Rabcnhorst speaks of observing 

 the contents of lieterocysts dividing up so as to form a little colony of cells, which 

 finally break through the maternal wall. I have only studied mounted specimens, 

 but have seen very clearly heterocysts in which this process was taking place. 



Hf. piinctatiiiu, Wood, (sp. nov.) 



N. terrestre ; tliallo expaiiso orbiculare vcl nonniliil irregulare, tenuissimo, jerngineo, parvo 

 niembrauaceo, pellucidulo; trichoiuatibus laxo intricatis, varie curvatis, articulis globosis vel 

 swpius ellipticia, plcrumque medio pellucidulis, laxe connexis ; cellulis perduraiitibus termi- 

 nalibus vel interjectis. 



Z)mm.— Cell, vegetat. tsbtjt" = -OOOIOG ; coll. pcrdur. j^J^s" = .00033. 



Hab. — In terrestre, New Jersey, (Prof. Austin.) 



Terrestrial ; thalliis expanded, irregular or orbicular, very thin, Ecruginous, small, membranous, 

 pellucid ; filaments loo.sely interwoven, variously curved, joints globose or often elliptical, 

 mostly pellucid iu the centre, loosely connected ; heterocysts terminal or interspersed. 



Remarks. — Mr. Austin has kindly sent mc the only specimens I have seen of this 

 species; they are labelled "Damp Ground, Sept." The fronds, which are often 

 aggregated, are very small and exceedingly thin, especially in their central por- 

 tions, where they are quite translucent ; in form they are often circular, some- 

 times quadrangular, sometimes quite irregular. As to size, most of them are not 

 more than two lines in diameter, some three, or possibly five lines. The margins 

 are often reflexed and thickened, especially in the smallest fronds. Two kinds 

 of filaments are visible ; 1st, those which I take to be in a perfected quiescent 

 state ; 2d, those which are in active growth. The former are composed of globose, 

 or more commonly elliptical joints, which are remarkable for the possession of a 

 central translucent, almost colorless spot, the endochrome apparently being arranged 

 in a ring around the outer part of the cell. This is, however, occasionally want- 

 ing. The filaments, which are in active growth, are very irregular in form, often 

 much broader than the others; their cells very irregular and sometimes fused 

 together into one mass. The measurements given in the diagnosis were taken 

 from the filaments of the first kind. 



h. Thallus indefinite expansus. 

 Thallus indefinitely expanded. 

 I¥. Cesatii, Bals. 



N. terrestre ; thallo longe latcque oxpanso, gelatinoso-merabranacco, viridi-flaveseente ; tricho- 

 matibus flexuoso-curvatis, sublaxe implicatis, pallida aerugineis ; articulis sphsericis, laxe vel 

 arctius connexis ; cellulis perduraatibus sphoericis, et interjectis et terminalibus. 



Z>mm.— Artie. .00016— .0002; cell, perdur.— .00033". 



Syn.—N. Cesatii, Bals. Rabenhorst, Flora Europ. Sect. II. p. 175. 



Hab.— In terrestre, Kansas (Prof. Parry) ; Texas (Prof. Ravenol). 



Terrestrial; thallus broadly and indefinitely expanded, gelatinous-membranaceous, yellowish- 

 green; filaments flexuously curved, rather laxly implicate, pale-greenish; articles spherical, 

 laxly or more closely connected ; heterocysts sjjhcrical, both interstitial and terminalibus. 



