244 FRESH-WATER ALG^ OF THE UNITED STATES. 



MASTIGONEMA FIBROSA, Wood. 



Light bluish -green, or olivaceous-green, apex of the ma- 

 ture filament prolonged into a long, distinctly articulated 

 hyaline seta ; sheath transparent ; in the immature filament 

 distally, broad, and distinct although hyaline ; below, rather 

 thick and close ; in the mature filament below close, indis- 

 tinct, above dissolved in fibrilla3 and wanting at the apex ; 

 heterocysts globose, sometimes geminate. 



Diameter of filaments, 10-11 //. 



Found growing with other low algae in a thick jelly, 

 which clothed some wet, dripping rocks. Appears to be 

 only one of the many varieties of this genus, not worthy of 

 a distinct name. 



Syn. Mastigotltrix fibrosa. Wood. 



Plate CLXXIV, fig. 8, four trichomes after W^ood. 



MASTIGONEMA FERTILE, Wood. 



Caespitose, intermingled with other algee ; filaments sim- 

 ple, elongate, truncate at the apex ; internal filament green, 

 often interrupted, sometimes articulate, sometimes not; 

 joints 2-3 times longer than the diameter ; sheath moder- 

 ately close, thick, firm, transparent and colorless, truncate 

 and open at the apex ; spores ( ? ) cylindrical, scattered, each 

 contained in a cell, frequently several in a filament ; hetero- 

 cysts globose, sometimes compressed. 



Diameter of filaments, about 8 yw. 



Found in stagnant pool in Bear Meadows, Pennsylvania, 

 forming a filamentous, felty mass with Oedogonia and 

 other algre. 



"The variously curved and interlaced, flexible filaments 

 are always simple and of uniform, or nearly uniform diam- 

 eter through their whole length. All specimens seen were 

 abruptly truncate. Wood. 



Seems a singular fact ; not one of these five forms discov- 

 ered by Wood came under our observation. 



Genus 83, ISACTIS, Thur. 



Filaments agglutinated by a more or less firm mucilage, often 

 calcariously incrusted, forming strata of flat surfaces, not arched, 

 filaments erect parallel, attached at the base. 



ISACTIS FLUVIATILIS, (Eab.) Kirch. 



Stratum turf or sod-like often extended, more or less with 

 a calcarious crust and then of an olivaceous gray color; 



