54 FRESH-WATER ALG^ OF THE UNITED STATES. 



Thallus at first subglobose, afterwards frequently fusiform, blackish-green, slippery, firm ; fila- 

 ments seruginous, very elongate, sometimes not articulated, but more generally shortly arti- 

 culated, sometimes strongly contracted at the joints ; apices sometimes truncate but generally 

 produced into a long, flexuous, translucent hair; sheath transparent,. close, frequently trun- 

 cate at the apex ; heterocysts globose or subglobose. 



Remarlcs. — This species grew in my aquarium on some brook-moss, which I 

 obtained from a spring above Manayunk. It forms little nodules of the size of a 

 pin's head upon the wire-like stems, or sometimes longer fusiform masses, which are 

 apparently produced by the coalescence of a number of the'little globes. The color 

 of these fronds, which are very firm, is a blackish-green. The filaments radiate from 

 the base in all directions, and at the apex are tipped with a very long hair-like flexu- 

 ous point, or they are truncate, apparently from the breaking off of this terminal 

 seta. The endochrome is not unfrequently interrupted within the sheath. When 

 it is articulated, the joints are usually about as long as broad, and frequently are 

 distinctly separated from one another. The sheath is sometimes quite apparent 

 and distinctly truncate and open above, but in other instances is with difficulty 

 perceived anywhere, and above is lost in the long hyaline point. At the points 

 of attachment of the frond the filaments are so densely crowded as almost to 

 appear to be coalescent, though I believe they are never really so ; yet it is often 

 almost impossible to separate them one from another by pressure on the glass cover, 

 without entirely mashing and distorting the filaments. 



Fig. 1 a, pi. 5, represents a section of a frond of this species slightly magnified; 

 fig. 1 5, a single filament magnified 460 diameters. 



Genus MASTIGOTHRIX, Ktz. 



Trichomata singula, plerumque sparsa, parasitica intra thallum Chsetophorarum aliarumque 

 algarum, flagelliformia, in apieem piliformem achroum hyalinum cuspidata, distincte articulata, 

 arete vaginata, basi cellula perdurante instructa. (R.) 



Filament single, mostly scattered, parasitic within the thallus of Chsetophora or other algse, 

 flagelliform, with the apex produced in a. hyaline hair, distinctly yaginate, furnished with a basal 

 heterocyst. 



Remarlcs. — I have simply copied the generic description of Prof. Eabenhorst, 

 although it seems to me more than doubtful whether the place of growth is any 

 generic character whatever. I have relied more on the long hyaline apical hair, 

 although our American form does grow in a gelatinous palmella like jelly. 



OT. fibrosa, Wood. 



M. dilute vel cseruleo-viridis, vel olivaceo-viridis, vel sub-seruginea, infra baud articulata, 

 sursum sEepe breve articulata, apice ia trichomata mtitura in setam hyalinam, distincte 

 articulatam, longam, producta; vaginis achroois — in filamcnto immaturo, supra distinctis, 

 latis, hyalinis, infra modice crassis, aretis, — in trichomata matura infra arctis, indistinctis, 

 supra in fibrillis dissolutis, apice absentibus ; cellulis perdurantibus globosis, interdum 

 geminis. 



Diam.— Trichone^f^V/; cell, perdnr. jsW— „^xni"- 



Syn.—M. fibrosa, Wood, Prodromus, Proc. Amer. Philos. Soc, 1869, p. 129. 



Hab. — Prope Philadelphia. 



