166 FRESH-WATER ALG^ OF THE UNITED STATES. 



for the very great thickness of the walls of the spore. There are two very appa- 

 rent coats separated by a thin not very evident one. The outer is the thickest ; 

 it is very thick, firm, and nearly colorless. The inner coat is of a decided orange- 

 brown. The parent-cells which give origin to these spores are slightly enlarged 

 in diameter. Sometimes the spores, instead of being elliptical, are irregular in 

 shape. 



Fig. 3 a, pi. 14, represents a sterile filament, magnified 250 diameters ; fig. 3, a 

 mature spore, magnified 450 diameters. 



Sp. insignis, (Hassall) Ktz. 



Sp. articulis sterilibus diametro 5-14 plo longioribus ; fasciis 2 (rarius 1-3), laxe spiralibus, 

 angustis, crenatis ; articulis fructiferis nonnihil tumidis ; cytiodermate utroque iine replicato 

 vel pi'otenso ; zygosporis rubido-bninneis, ovato-ellipticis. 



IHam.--0.001b". 



Syn. — Zygnema insigne, Hassall, Fresh-Water Algae, p. 440. 



Spirogyra insignis, (Hassall) Kutzing. Rabenhorst, Flora Europ. Algarum, Sect. 

 III. p. 235. 



Hob. — In stagnis, prope Philadelphia. 



Sterile joints 5-14 times longer than broad ; chlorophyl filaments mostly 2 (rarely 1-3), laxly 

 spiral, narrow, crenate ; fertile joints somewhat enlarged ; cytioderm at each end folded in 

 or produced ; zygospores reddish-brown, ovate elliptical. 



Eemark. — Fig. 6, pi. 16, represents this species. 



6. Gytioderma cellulae fine neo protensum nee replicatum. 



Cytioderm not infolded in the end of the cell. 

 * Fasciae spirali unicse (raro duae). 

 Chlorophyl band single (rarely two). 

 Sp. longata, (Vauch.) Ktz. 



Sp. dense csespitosa, Isete luteolo-viridis, valde lubrica; articulis sterilibus diametro 2-6 plo 

 longioribus, fertilibus saape tumidis abbreviatis ; fascia spirali lata, dentata ; anfractibus sub- 

 laxis 2-5 ; zygosporis ellipticis. 



Biam.—O.OOl". 



Syn.— Gonjugata longata, YAtroHER, Histoire des Conferves d'Eau douce, p. tl. 



Sp. longata, (Vauoh.) Kutzing. Rabenhorst, Flora Europ. Algarum, Sect. III. p. 238. 

 .Ea6.— In stagnis, prope Philadelphia ; Wood. Rhode Island ; (S. T. Olney) Thwaites. 

 Densely csespitose, bright yellowish-green, very slippery ; sterile joints 2-6 times longer than 



broad ; fertile articles swollen, often abbreviate ; chlorophyl filaments broad, dentate ; turns 



of the spiral somewhat loose, 2-5 ; zygospores elliptical. 



i?emarA;s.— According to Prof. Rabenhorst, this species attains in Europe a 

 diameter of .0011" and the cells a length of 8 times their breadth. The same 

 authority also describes the fertile cell as being either not swollen, or moderately 

 so (" aut non aut modice tumidis"). In all the specimens of our American forms 

 which I have seen, the sporangial cells are very decidedly swollen. 



Fig. 4, pi. H, represents portions of sterile filaments, magnified 250 diameters, 

 and fig. 4 a, a part of a fertile pair of filaments containing immature spores enlarged 

 260 diameters. 



