FRESH-WATER ALG^ OE THE UNITED STATES. 63 



singly since I haye examined some hundreds of specimens, and have only in one 

 instance detected them in pairs. The apices of the branches, and indeed of 

 the main filaments, are beautifully colorless and hyaline, and not unfrequently a 

 branch will have this hyaline sheath for a long distance. The extreme ends are 

 mostly truncate and open, and, often near them, the sheaths will have marked 

 swellings ; a condition which, for want of a better term, I have spoken of as being 

 barbate. Sometimes near the end of the filament the diameter of the sheath will 

 be suddenly lessened. The large cells are both interstitial and placed at the bases 

 of the branches ; they are more or less oblong or quadrangular, sometimes 'being 

 scarcely longer than broad, but in other cases several times longer. At their posi- 

 tion there is very generally a sort of globular enlargement of the filament. The 

 sheath is sometimes very obscurely lamellate. The color of the older filaments is 

 a dark, almost chocolate-brown. This is apparently the species referred to by 

 Professor Bailey as being Scytonema ocellatum of Harvey, in Silliman's Journal,, vol. 

 iii. N. S., although that plant, according to Professor Rabenhorst, belongs to the 

 genus Sirosiphon. 



Fig. 1 a, pi. 7, represents a portion of a filament, magnified 280 diameters ; fig. 

 1 J, a whole filament slightly magnified. 



S. dubinm, Wood (sp. noT.) 



S. immersum, in floccis mucoso-tomentosis olivaceo-nigris plantas aquaticas adhserens, vel in 

 strato mucoso et nonnihil tomentoso dispositum; trichomatibus valde elongatis et arete in- 

 tricatis, varie curvatis, plerumque sparse pseudoramosis ; pseudoramulis plerumque singulis, 

 etplus minus distantibus et modice brevibus, vel interdum brevissimis et abortivis et nonnihil 

 confertis; trichomatibus internis saepe in pseudocellulis distinctis contentis, interdum con- 

 tinuis et indistincte articulatis vel inarticulatis, plerumque dilute c89raleo-viridibns sed inter- 

 dum Isete serugineis, subtiliter granulatia; vaginis arctis plerumque modice crassis et firmis, 

 hyalinis, coloris expertibus; cellulis perdurantibus cylindricis, diametro 2-6 plo longioribus. 



Diam.— Cam vag. ^^^j-^" —j^^^^" =■. .00026"— .0004". 



Hah. — In aqnis quietis, Cumberland County, New Jersey. 



Immersed, adhering to water plants in olive-black tomentose flocculent masses, or arranged 

 in a mucous and somewhat tomentose stratum ; trichomata very long and closely interwoven, 

 variously curved, mostly sparsely branched ; branches generally single, more or less distant, 



• and moderately short, sometimes very short, abortive, and somewhat crowded ; internal fila- 

 ment often contained in distinct cell-like apartments, sometimes continuous and indistinctly 

 articulate, or not at all articulate, finely granulate, mostly a pale bluish-green, sometimes a 

 bright aeruginous color ; sheath close, mostly rather thick and firm, hyaline colorless ; hetero- 

 cysts cylindrical, 2-6 times longer than broad. 



Remarks. — I found this plant, September, 1869, in Shepherd's Mill Pond, near 

 Greenwich, Cumberland County, New Jersey. It formed dark, ugly, somewhat 

 slimy, tomentose flocculi adhering to, and binding together, the finely-dissected 

 leaves of Ranunculus aquatilis. The filaments are very long, slender, and sparsely 

 branched. The branches are given off at right angles, or nearly so, but are fre- 

 quently sharply bent just above their origin. They are often, but not always, 

 rather short. The most remarkable character that the plant possesses is that in 

 many filaments there are very distinct regular partitions stretching across from 



