FRESH-WATER ALG^ OF THE UNITED STATES. 171 



Fig. 3. a, pi. 15, represents part of a sterile filament of this species; 3 I, portion 

 of a pair of fertile filaments, both magnified 125 diameters. 



Sp. crassa, Xtz. 



Sp. laete viridis, denique sordide viridis ; articulis sterilibus diametro snbsequalibus, post divi- 

 sionem interdum fere ^ plo brevioribus, ante divisionem ssepe fere 2 plo longioribus ; cytio- 

 dermate tenui, homogeneo, utroque fine nee protenso nee replicato ; fasciis spiralibus 4, 

 dentatis vel tuberculatis, saepe arctis, subtransversis, tenuibus ; anfractibus 1^-4 ; cellulis 

 fructiferis aliis simillimis, baud inflatis ; zygosporis globosis vel ellipticis. 



Diam. — Max. .0065." 



Syn. — Sp. crassa, Ktz. Rabenhorst, Flora Europ. Algarum, Sect. III. p. 246. 



Hah — In stagnis, prope Philadelphia. 



Bright green, but finally a dirty green ; sterile articles about as long as broad, sometimes after 

 division only half as long, sometimes before division twice as long; cytioderm thin, homo- 

 geneous, not infolded or produced at the ends ; spiral filaments 4, dentate or tuberculate, 

 often close, subtransverse, thin ; turns from IJ to 4 ; fertile cells very like the others, not 

 infiated ; zygospores globose or elliptical. 



BemarJcs. — This species is very common in the neighborhood of this city, occur- 

 ring in springs, &c., but especially in the ditches in the Neck. It forms long, 

 lubricous masses, of a bright green color, readily distinguishable by the size of the 

 filaments, which are separated with ease by the unaided eye. I have gathered it 

 repeatedly, in fruit, from the middle of April to the middle of June. In this state 

 the mass has lost its bright green color, and when the filaments are closely examined, 

 even without a glass, minute dark points mark the positions of the spores. 



Fig. 4 a, pi. 15, represents part of a filament commencing reproduction; 4 6, fila- 

 ments which have matured the spores ; 4 c, a pair of conjugating filaments. 



Genus ZYGNEMA. 



Cellulae vegetativae cylindricsB. Massa chlorophyllacea initio effusa et subhomogenea, postea dis- 

 tincte granulosa aut per cellulae lumen distributa, granula amylacea duo centralia involvens, aut in 

 corporibus duobus (in quaque cellula) plus minusve distincte stellatim radiantibus juxta nucleum 

 centralum granum amylaceum unioum involventibus collocata. Conjugatio scalariformis vel late- 

 ralis. 



Tegetative cells cylindrical. Chlorophyl masses in the beginning effused and subhomogeneous, 

 afterwards distinctly granular, either distributed throughout the cavity of the cell, involving two 

 central starch granules, or gathered together into two masses (in each cell), with more or less dis- 

 tinctly stellate radii and a central starch granule placed near the nucleus, one on each side of it. 



Z. insigne, (Hassall) Ktz. 



Z. csespitibus et plerumque natantibus vel in aqua diffusis, saturate viridibus vel saepe sordide 

 flavo-viridibus ; articulis sterilibus diametro circiter squalibus vel duplo longioribus ; conju- 

 gatione scalariforme (et saepe simul laterali, R.); zygosporis globosis; sporodermate laevi. 



Biam.— Cell -^ AW = -00126" ; spor. tAV'—tiVW = 0.00093"— 0.00016". 

 Syn. — Tyndaridea insignis, Hassall, Fresh-Water Algae, vol. i. p. 163. 



Zygnema insigne, (Hassall) Kutzimg. Rabenhorst, Flora Europ. Algae, Sect. III. 

 p. 249. 

 J3a6.— In stagnis, prope Fhiladelphia ; Wood. Rhode Island ; (S. T. Olney) Thwaites. 



