20 FRESn-WATER A L CwE OF THE UNITED STATES. 



W'lu'ii grown in a hotlli-, tin- plant appears as a very thin stratum growing np tlie 

 sides. The agreement uf this phmt with the descriptions of the European 0. Umosa 

 is very close, so that I do not think it can be separated from it, although in 0. 

 Umosa the dissepiments are said to be distinctly granular. 



Fi<^. 4, pi. 1, represents a tilamcnt of the American plant magnified 1250 dia- 

 meters. The color and form are closely counterfeited, but the characteristic sepa- 

 ration of the endochrome into parts at the joints is decidedly exaggerated. 



O. iicgiccia, Wood. 



O. trichomatibiis niodice brevibus, aut dilute purpuraceo-plumbeis aut plumbeo-cinereis, pler- 

 umque rectis, aut stratum mucosura atro-purpureum baud distincte radiante fonnantibus, aut 

 in strato gclatinoso baud radiante subplumbeo dispersis et cum algis aliis intermixtis, rare 

 oscillantibus sed lente sesc moventibus; articulis diametro fere 4 plo brevioribus ; dissepi- 

 moutis plerumque baud granulosis, rare iudistincte granulosis; apiculo obtuse rotuudalo, 

 interdum breviter nonuibil attenuate. 



Syn. — 0. neglecla, Wood, Prodromus, Proc. Amer. Philos. See, 1869, 124. 



Diam. — xsVif ' = 0066. 



Hab. — In stagnis prope Philadelphia* 



Filaments rather short, of a dilute purplisli-lead color, or leaden-gray, generally straight, either 

 forming a mucous, blackish-purple stratum without marked rays, or diffused with other algaj 

 in a gelatinous mass, rarely oscillating but gliding; articles about four times shorter than 

 broad ; joints for the most part not granulate, rarely indistinctly granulate ; ends obtusely 

 rounded, occasionally short, somewhat attenuate. 



Rcmarhs. — I have found this plant in the shallow ditches along the track of the 

 Norristown Railroad above Manayunk, growing in two dift'erent ways. In the one 

 it forms a distinct, soft, gelatinous, floating stratum of a very dark purplish color, 

 consisting of nothing but interwoven filaments, and provided with long rays. In 

 the other, the plant is largely mixed with diatoms and other alga; into a thick, 

 gelatinous stratum without rays, whose color is a dirty slaty tint, which, however, 

 is not all distinctive, and often varies as the proportion of the diff'erent constituents 

 varies. The color of the single filaments is a slaty, almost neutral tint. The 

 cytioplasm is remarkable for the numerous very minute spots more transparent and 

 with less color than the surrounding parts. The ends of the filaments are often 

 abruptly obtuse, frequently however there is a very short taper. Motion does not 

 appear to be very active, and seems especially to be gliding, rather than a bend- 

 ing to and fro of filaments. 



Fig. 5(«, pi. 2, is an outline drawing of a filament magnified 450 diameters ; 56 

 is a portion of a filament. 



©. iinpcratoi*, Wood. 



0. m strato mucoso, plerumqne natante, olivaceoatro, longe radiante; trichomatibns rectis aut 

 subrectis, tranquillis, dilute viridibus vel saturate olivaceis, baud oscillantibus, sed ambulan- 

 tibus; apiculis nonnihil attenuatis, late rotnndatrs vel subtruncatis, curvatis ; articulis diame- 

 tro 5-12 plo brevioribus, ad gcnicula indistincte contractis ; cytioplasiuate homogeueo, 

 olivaceo-viride; vaginis firmis, ad genicula distincte transverse striatis. 



Syn.—O. imperator, Wood, Prodromus, Proc. Aracr. Pbilos. Soc, 1869, 124. 

 Diam.— .002". 



