252 FRESH-WATER ALG^ OF THE UNITED STATES. 



Diameter of filaments, 12-20 //. 



Diameter of branchlets, 10-16 u. 







Syn. Scytonema immersum, Wood. 

 Frequent in ponds, floating. 



Plate CLXXXIII, figs. 8-10, three fragments of filaments. 

 Branchlets usually very long. 



SCYTONEMA NAEGELII, Kg. 



Dull aeruginous to cinereous; floccoso-caespitose, about 

 three lines long; ^sewZo-branchlets most frequently gemi- 

 nate, much thinner at the base than the stem, but quickly 

 enlarging ; articulations short, 3-4 to diameter, often inclin- 

 ing in the sheath, now and then interrupted. Sheath close 

 and thin, colorless or light brown. Heterocysts oval. 



Diameter of filaments, 14-18 JJL. 



Occurs on moist rocks, unlike the European form which is 

 found submerged. 



Plate CLXXXIII, figs. 11-13, representations of three 

 filaments. 



SCYTONEMA CATARACTA, Wood. 



Forming on rocks an extended turf-like stratum of brown- 

 ish black color ; filaments flexuous, flexible, long ; irregu- 

 larly branched, their surface smooth ; branches elongate, 

 singly or in pairs; sometimes fuscous, frequently hyaline, 

 their apices rounded, rarely somewhat attenuate, frequently 

 provided with enlargements; cytioplasm aeruginous, gen- 

 erally distinctly articulate; articles mostly shorter than 

 broad, but sometimes longer; frequently disjoined, some- 

 times subglobose ; sheaths thick and firm. Heterocysts 

 interjected and mostly single. 



Diameter of filaments, with sheath, 12-16 yu, rarely 25 /<. 







Syn. Scytonema Brandegei, Wolle. 



Abundant on rocks below the great Niagara Falls. 



Received specimens from C. Brandegee, collected on the 

 Rocky Mountains, evidently the same species but many of 

 the filaments much larger, measuring 38-42 // in diameter, 

 but forming the same dark turf-like stratum. 



Plate CLXXXIII, figs. 1, 2, from Rocky Mountain speci- 

 mens ; figs. 3, 4, Niagara specimens. 



SCYTONEMA MYOCHROUS, Ag. 



Strata thin, pannosely tomentose, obscurely fuscous or 

 olivaceous, often with a silky gloss ; filaments strong, fus- 



