tapering to a fine point distally; vegetative cells very short, 5-8/* 

 in diameter, 2-4/x long, or quadrate; heterocysts subglobose or 

 hemispherical, 8-10/a in diameter; filaments 10-14/a wide at the base. 

 On moist earth or attached to or entangled among filamentous 

 algae. Mich., Wis. 



RIVULARIA (Roth) C. A. Agardh 1824, p. 19 

 Filaments semiparallel or radiately arranged in copious, very 

 firm mucilage, forming either semi-microscopic globose colonies or 

 macroscopic, bullate or expanded masses which may be either solid 

 or hollow; heterocysts all basal and the trichome tapering from 

 them to fine points; frequently branched, the branches sometimes so 

 disposed as to form transverse zones through the colonial mass; 

 individual sheaths definite at the base but becoming diffluent toward 

 the apex of the filament; gonidia lacking. 



Key to the Species 



Cells 4-7.5/Lt in diameter; colonies lime encrusted __. R. haematites 



Cells 9-12. 5/i in diameter; colonies not conspicuously lime encrusted R. niinutula 



Rivularia haematites (D. C.) C. A. Agardh 1824, p. 26 

 PI. 131, Figs. 10, 11 



Filaments united in attached, hemispherical colonies, inclosed by 

 a firm mucilage and encrusted with lime, colonies frequently gre- 

 garious and agglutinated to form an expanse as much as 3 cm. 

 thick; filaments closely arranged and semiparallel, the false branches 

 forming transverse tiers or zones; individual sheaths conspicuous 

 below, firm and close, either colorless or yellow, becoming expanded 

 and funnel-fomn above toward the periphery of the colony; cells 

 4-7. 5/i, in diameter, twice the diameter in length in the lower part 

 of the trichome, becoming % as long as wide in the apical region. 



On stones in lakes and flowing water. Mich. 



Rivularia minutiild ( Kuetz. ) Bornet & Flahault 1886, p. 348 



PI. 136, Fig. 9 



Filaments arranged in brownish, globular or hemispherical 

 colonies, enclosed in firm mucilage, but rather loosely and radiately 

 arranged within the colony and inclosed in wide, hyaline or brown- 

 ish, lamellate sheaths, becoming funnel-form toward the periphery 

 of the colony; trichomes tapering to a stout hair above from oblong 

 or hemispherical heterocysts; cells 9-12.5/i in diameter, quadrate 

 below, becoming 3-4 times as long as wide in the apical region. 



Attached to submerged plants and wood. Mich. 



[556] 



