18 FRESH-WATER ALG^ OF THE UNITED STATES, 



O. chlorina, KiiTziNo. 



0. interdum in strato sordide viridi natante, interdum in aqua diffusa ; trichomatibus rectis, 

 yivide moventibus, vel articulatis et cum cytioplasmate granulate, vel inarticulatis et cum 

 cytioplasmate baud granulate; cytioplasmate hyaline, interdum coloris fere expertibus, 

 interdum dilutissime viride ; apiculo baud attenuate, ebtuse rotundato, recto ; articulis dia- 

 metro subsequalibus. 



Diam.—jT;\:s"—vsW = .00014"— .0001". 

 Hab. — In stagnis prope Philadelpbia. 



Sometimes swimming en the water as a dirty-greenish stratum, sometimes diffused in the water; 

 filaments straight, actively moving, either articulated and having the cytioplasm filled with 

 blackish granules, or else neither articulate nor granulate, cytioplasm hyaline, almost colorless, 

 or with a faint greenish tint ; ends of the filaments not attenuate, straight, obtusely rounded ; 

 joints about equal to the diameter. 



RemarTes. — I found this species in the month of August, 1869, in one of the 

 stagnant brick-ponds below the city. It occurred as a sort of floating scum, or 

 else diffused through the water, which was then opaque and greenish. It resembled 

 so a protococcus in gross appearance that I did not think of its being an oscilla- 

 toria until I placed it under the microscope. The filaments are almost colorless, 

 and, in most instances, are very distinctly granulate and articulate. The dissepi- 

 ments are in such cases clear and transparent, perfectly free from granules. This 

 form is very close to the descriptions of the European 0. chlorina, Ktz., but differs 

 somewhat from descriptions, chiefly in habit of growth. The filaments, when in 

 mass, are often seen to be curved under the restraining force of the glass cover, 

 but when free I think always straighten themselves. 



Fig. 1, pi. 1, represents a single filament, magnified 750 diameters. 



O. Frohlichii, Ktz. ? 



O. strato indefinite, tenue, viride ; trichomatibus Isete viridibus, subrectis, vivide oscillantibus; 

 ad genicula nonnihil pellucidis et leviter' contractis et rarissime granulatis; articulis diametro 

 2, 3, 4 pie brevioribns ; cytioplasmate obscure aut distincte minutissime granulate ; apiculo 

 hand attenuate, late rotundato. 



Diam.— ^gVir"— teW = 0.00066"— 0.0004. 

 Hab. — In flumine Schuylkill. 



Stratum indefinite, thin, green ; filaments bright green, straightish, vividly oscillating, some- 

 what pellucid at the joints, where they are slightly contracted and very rarely granulate ■ 

 articles 2, 3, 4 times shorter than the diameter, cytioplasm obscurely or distinctly very mi- 

 nutely granulate ; apex net attenuate, broadly rounded. 



Bemarhs.—l found this species growing upon the bottoms of the shallows in the 

 Schuylkill Eiver and its larger tributaries, forming a somewhat badly defined 

 stratum, rather, indeed, a coating on the mud than a definite stratum. The motion 

 is exceedingly active, the filaments bending and gliding, and their apices con- 

 stantly curling and extending in all directions. The apices are very blunt. The 

 filaments are not often seen woven and twisted together into a mass composed 

 simply of themselves, but are stuck together loosely, each filament remaining 

 straightish, with numerous little masses of mud between them. I have not been 



