with 1 pyrenoid, lying along the transverse wall. Filament inclosed 

 by a broad gelatinous sheath through which fibrillar concretions 

 radiate to the periphery. 



Key to the Species 



1. Cells transversely ellipsoid or subquadrate, arranged to form 

 a long continuous filament, inclosed in a relatively narrow 

 sheath; cell wall halves not apparent R. fiavescens 



1. Cells a different shape from above, not forming 



a continuous simple filament 2 



2. Cells transversely lenticular, pointed at the poles, separated from 

 each other in a wide, gelatinous sheath, sometimes irregularly 

 arranged, forming filaments with anastomosing branches; 



cell wall halves not apparent R. irregulare 



2. Cells spheroidal, evenly spaced and separate from each other; 

 cell wall halves evident, forming a transverse rim around 

 the cell R. conjunctivum 



Radiofilum conjunctivum Schmidle 1894, p. 48 

 [R. apiculatum West & West] 



PI. 7, Fig. 6 



Filaments short, fragmenting readily, composed of spheroidal cells 

 in a wide gelatinous sheath. Cell walls formed by 2 cup-shaped 

 halves adjoined in the midregion and forming a rim which produces 

 an apiculation at each side of the cell. Chloroplast a parietal plate 

 lying along the end wall. Cells Gjx in diameter, 4-6[jl long. 



Very common in a large number of lakes and swamps, especially 

 in soft water and acid habitats, hence often associated with desmids. 

 Mich., Wis. 



Radiofilum fiavescens G. S. West 1899, p. 57 

 PL 7, Fig. 10 



Filaments long, composed of transversely ellipsoidal or subquad- 

 rate cells in a narrow gelatinous sheath in which radiating fibrils 

 are apparent. Chloroplast a parietal plate. Cells 6.8-15/* in diam- 

 eter, 5-10;a long; filament 9-25|U wide, including sheath. 



Some specimens in our collections are larger than the dimensions 

 usually reported for R. fiavescens, and have cells that are often def- 

 initely subquadrate. It is possible that such an expression justifies a 

 separation to form a new species. The shape of the cell in this species 

 is known to vary, however. 



Scarce; in a few soft water lakes and in Sphagnum bogs. Mich., 

 Wis. 



[103] 



