FRESH-WATER ALG^ OF THE UNITED STATES. 19 



able to identify the species positively, but have referred it with doubt to 0. Frohli- 

 cliii. 



Fig. 2, pi. 1, represents the end of a filament. 



O. nigra, Vauoh. 



0. strato plus minus compacto, amplo, plerumque natante, atro-viride, cum radiis longis ; tricho- 

 matibus plerumque flexuosis; apice obtuse rotundato ; articulis diametro f plo brevioribus; 

 dissepiraentis distincte granulatis ; cytioplasmate pallide csesio. 



Hah. — In fossis stagnis propc Philadelphia. 



Stratum more or less compact, ample, broad, mostly floating, blackish-green, with long radii ; 

 filaments mostly flexuous ; apices obtusely rounded; joints f shorter than broad; dissepi- 

 ments distinctly granulate ; cytio^plasm pale-grayish. 



Remarlcs — This species is found in thick, rather loose strata, floating, especially 

 vphen old, on stagnant waters, or adhering to plants, &c., or the muddy shores and 

 bottom of ditches, foul aquaria, &c. The color of the stratum is a very dark 

 blackish-green, with a peculiar, glossy, repulsive appearance. The single filaments 

 are of a pale-bluish neutral tint, sometimes a little greenish, very much curved 

 and entangled, or more rarely straightish. Their motion is active. The measure- 

 ments do not quite equal those given by European authorities, but otherwise the 

 plant agrees well with their descriptions. 



Fig. 3a, pi. 1, represents the mass of the plant as seen with the naked eye; fig. 

 36, shows a number of filaments slightly magnified; fig. Ic, a broken portion of a 

 filament magnified 260 diameters, with the sheath projecting beyond the endo- 

 chrome ; fig. Id, the end of a filament still more highly magnified. 



O. limosa, Agardh. 



0. trichomatibus subrigidis et subrectis, vivide oscillantibus, csBruleo-viridibus, in stratum muco- 

 sum laete saturate viride et raodice longe radians et natans collectis et intertextis, distincte 

 artieulatis ; articulis diametro subsequalibus, interdum duplo brevioribus (post divisionem), 

 ad genicula distincte constrictis ; dissepimentis hand granulatis ; apiculo obtuso, hand atten- 

 uato, interdum recto, interdum curvato ; cytioplasmate granulato. 



Diam.—^-^iBs" 



Hob. — In stagnis prope Camden, New Jersey. 



Filaments straightish and somewhat rigid, vividly oscillating, bluish-green, interwoven into a 



bluish-green, floating stratum, with moderately long radii, distinctly articulate; articles about 



equal to the diameter, or after division one-half shorter, at the joints distinctly constricted ; 



dissepiments not granulate; apices obtuse, not attenuate, sometimes straight, sometimes 



curved ; cytioplasm granulate. 



Remarhs. — I have found this species floating on foul ditches near Kaighn's 

 Point, New Jersey, in the month of May. The color of the stratum is a very pure 

 deep-green; the single filaments vary from a rather bright deep-green to a pale blue- 

 wreen, according to the power under which they are seen. The apices are not at all 

 attenuate. The constriction at the articles is scarcely visible with a lower power than 

 ^th. The stratum is rather thin, with a good deal of dirt adhering to its bottom. 



