168 FRESH-WATER A L G M OF T II E UNITED STATES. 



globosis aut ovalibus, aut subcylindricis, diametro tcqualibus aut | plo longioribus; articulis 

 fertilibus cylindricis, baud tumidis. 



Diam.-A.rl. stcril. T l/ = .002; spor 7 |g T " .002". 



gyn. Sp. dubia, KUTZING. RABENHORST, Flora Europ. Algarum, Sect. III. p. 243. 



Hab. In stagnis, prope Philadelphia. 



Green, in fruit light green; sterile joints cylindrical, 1^-2 J times longer than broad; spiral 

 filaments 2-3, very narrow, nodose, lax, turns 1-2; cytioderin neither infolded nor protruded 

 at the end, rather thick ; zygospores polymorphous, either subglobose, oval, or subcylindrieal, 

 as broad as long to f times longer ; fertile articles cylindrical, not enlarged. 



Remarks. I have found this species growing in the ditches below the city, fruit- 

 ing abundantly in May. When in this condition it forms masses of a dirty, lightish, 

 yellowish-green. The spores mostly fill pretty well the fertile cells. My specimens 

 do not agree completely with the descriptions given of the European. The two 

 forms, however, completely overlap one another, except in one character, namely, 

 the shape of the sporangial cell. I have never seen it swollen or at all tumid in 

 American specimens, whilst in the European it is said to be " modice tumidis." 

 This difference alone does not, however, seem to me sufficient to characterize a 

 new species. I have seen specimens of this plant collected by Dr. Lewis at Cobble 

 Mountain. They agree well with the Philadelphia specimens, except in attaining 

 a little larger size, .0021", and in the sterile filaments having their walls very thick. 

 The character of non-inflation of sporangial cells is perfectly preserved. 



Fig. 4, pi. 17, represents this species. 



Sp. ri vulari*, (HASSALL) RABENH. (non KTZ.) 



Sp. saturate viridis, lubrica; articulis sterilibus diametro 7-11 plo longioribus; fertilibus cylin- 

 dricis aut vix tumidis; cytiodermato tcuuissimo, utroque fine nee protenso nee rcplicato, 

 fasciis 4, laxe spiralibus, modice angustis, nodulosis et serratis, anfractibus 2 ; zygosporis 

 ellipticis, diametro 2-2| longioribus. 



Diam. Art. ster. rfas"iW = .0012" .00146" ; spor. T J8/ ri8 ff ". 

 Syn. Zygnema rivularis, HASSALL, Fresh-Water Algas, vol. i. p. 144. 



Spirogyra rivularis, (HASSALL) (non KUTZING) RABENIIORST, Flora Europ. Algarum, 

 Sect. III. p. 243. 



Hab. In rivulis, Florida ; (CANBY) WOOD. 



Deep green, slippery ; sterile articles 7-11 times longer than broad, fertile cylindrical or slightly 

 tumid ; cytioderm very thin, neither infolded nor protruded at the end ; chlorophyl filaments 

 4, laxly spiral, moderately narrow, nodose and serrulate, turns 2 ; zygospores elliptical, 

 2-2 times longer than broad. 



RemarJcs. This species was collected by Mr. Wm. Canby in Pine Barren Run, 

 near Hibernia, Florida. It is rather smaller than the European forms, but docs 

 not appear to be distinct from them. Rabenhorst, indeed, states that there are 

 only two or three, chlorophyl spiral bands in a cell, but Hassall in the description 

 of the type states distinctly that in some instances there are four bands, and also 

 figures the plant so. 



Fig. 5 a and 6, pi. 17, represents sterile cells of this species, magnified 260 



