FRESH-WATER ALQJE OF THE UNITED STATES. 57 



The second class of characters are those discoverable only with the higher powers. 

 They are divisible into two sets ; those aiforded by the inner filament and those 

 derived from the sheaths. In the first of these the points to be noted are, the 

 diameter of the filament ; its color, whether it be or be not articulated, and if it 

 be the length of the joints ; whether it is uniform or moniliform ; , whether it be 

 homogeneous or granulate ; then the heterocysts should be examined as to their 

 size, position, arrangement, shape, number, and color. 



The diameter of the sheath, its homogeneousness, its color, firmness, and the 

 condition of its outer surface are to be included in the specific study. 



Genus SCYTONEMA. 



Triciiomata casspitoso-congregata vel fascieulata, plus minus pseudoramosa, cellulis interstitialibus 

 instructa ; vaginae gelatinoso-membranacese, e stratis (interdum obsoletis) pluribus cylindraceis com- 

 positffi; cellulis perdurantibus singulis. 



Filaments caespitosely-congregate or fasciculate, more or less pseudoramose ; furnished with in- 

 terstitial cells ; sheaths gelatinous-membranaceous, composed of many cylindrical, sometimes ob- 

 solete, strata ; heterocysts single. 



a. Terresires vel aquaticae. 

 a. Terrestrial or aquatic. 



S. sin:plice, Wood, (sp. nov.) 



S iu strato modiee crasso, subtomentoso, nigro-viride ; trichomatibus valde elongatis, flexuoso- 

 curvatis, parcissime pseudoramosis vel ssepe sine pseudoramulis ; pseudoramulis geminis vel 

 singulis, plerumque elongatis ; trichomatibus internis modo distincte articulatis, raodo inar- 

 ticulatis, apice interdum brevissime articulatis, granulosis, pallide viridibus, ad genicula saBpe 

 Dodosis vel disjunctis, articulis plerumque diatnetro sequalibus ad 7 plo lougioribus; vaginis 

 plerumque supra truncatis et apertis, pellucidis, sspe coloris expertibus, interdum dilute 

 aureo-brunneis ; cellulis perdurantibus cylindricis, interjectis, diametro 2-5 plo longioribus. 



Diam.—Trich. cum vag. ^f^VV'— ttW = .0004"— .00066"; sine vag. ^^^^"—^f^^" = .00013" 

 —.00026" 



Eab. — In lignis irroratis. South Carolina. (Ravenel.) 



S. in a moderately thick, somewhat tomentose, blackish-green stratum; trichomata very elongate, 

 flexuously curved, very sparsely branched or frequently vyithout branches ; branches geminate 

 or single, mostly elongate ; internal filament partly distinctly articulate, partly inarticulate, 

 granular, pale-greenish, in its apex sometimes»very shortly articulate, sparsely granular, 

 often nodose or disjoined at the joints ; articles mostly from equal to to 7 times longer than 

 the diameter; sheaths thick, transparent, often colorless, sometimes pale yellowish-brown, 

 mostly open and truncate at apex ; heterocysts cylindrical, interspersed, 2-5 times longer 

 than their diameter. 



Remarhs. — I am indebted to Professor Eavenel for specimens of this species. 

 They are preserved in solution of acetate of alumina and accompanied by the fol- 

 lowing label : " Adhering to the wet sides of a wooden gutter, leading water from 

 a spring, September 29, 1869: Aiken, South Carolina." Tlie filaments are 

 remarkable for the fewness of their branches. Generally, indeed, there are no 



8 May, 1872. 



