166 FRESH- WATER A L G YE 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 nomiihil tumidis ; cytiodermate utroquc fine replieato 

 vel protenso ; zygosporis rubido-brunneis, ovato-ellipticis. 



Diam. 0.0015". 



Syn. Zygnema insigne, HASSALL, Fresh-Water Algae, p. 440. 



Spirogyra insignis, (HASSALL) KUTZINQ. UABENHORST, Flora Europ. Algarum, Sect. 



III. p. 235. 

 Hub. 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 ; cytiodenn at each end folded in 

 or produced ; zygospores reddish-brown, ovate elliptical. 



BemarJc. Fig. 6, pi. 16, represents this species. 



b. Cytioderma cellulsefine nee protensum nee replicatum. 



Cytioderm not infolded in the end of the cell. 

 * Fasciae spirali unices (raro duse). 



Chlorophyl band single (rarely two). 

 Sp. longata, (VAUCH.) KTZ. 



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

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

 laxis 2-5 ; zygosporis ellipticis. 



Diam. 0.001". 



Syn. Conjugala longata, VACCHER, Histoire des Conferves d'Eau douce, p. 11. 



Sp. longata, ( VAUCH.) KiliziNG. RABENHORST, Flora Europ. Algarum, Sect. III. p. 238. 



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



Densely caespitose, 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. 



Remarks. 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. 34, 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. 



