134 Minnesota Algae 



apical cell tapering, obtuse; cells 4.5-12 mic. in length; cell contents gran- 

 ulated, blue-green. 



North America. (Trecul, Anderson). South Carolina. On clayey- 

 soil in damp "Black-jack" woods. Chester. January 1898. (Green). West 

 Indies. (Lenormand). 



Genus HYDROCOLEUS Kuetzing. Phyc. Gen. 196. 1843. 



Plant mass forming a caespitose cushion, very rarely hardened with 

 calcium carbonate, or caespitose but somewhat indefinite, or even not 

 at all caespitose, but Phormidium-like; sheaths always colorless, cylindri- 

 cal, somewhat lamellose, more or less mucous or somewhat amorphous, 

 later entirely diffluent; trichomes few within the sheath, often loosely 

 aggregated; apex of trichome straight, more or less tapering, capitate; 

 outer membrane of apical cell thickened into a calyptra; cells shorter than 

 the diameter of the trichome, in some species very short. 



I Plants living in salt water. 



1 Plant mass caespitose 



(i) Plant mass green becoming violet; sheaths cylindrical, moderate- 

 ly mucous; trichomes 14-21 mic. in diameter 



H. comoides 

 (2) Plant mass blackish green; sheaths irregular in outline, strongly 

 mucous; trichomes 18-24 ™ic. in diameter 



H. cantharidosmu; 



2 Plant mass caespitose or forming an expanded mucous stratum, 



blackish green; sheaths irregular in outline, strongly mucous or 

 even entirely diffluent; trichomes 8-16 mic. in diameter 



H. lyngbyaceus 



3 Plant mass mucous 



(i) Plant mass yellowish brown or dull green; sheaths somewhat 

 amorphous or entirely diffluent; trichomes 14-21 mic. in diame- 

 ter H. glutinosus 



(2) Plant mass pale blue-green; sheaths agglutinated, forming a dif- 

 fluent, amorphous layer; trichomes 25-30 mic. in diameter 



H. holdenii 



II Plants living in fresh water 



1 Trichomes 6-8 mic. in diameter; apex of trichome gradually taper- 



ing, evidently capitate; cells somewhat quadrate or one-half the 

 diameter of the trichome in length H. homoeotrichus 



2 Trichomes 12 mic. in diameter; cells quadrate or two or three times 



shorter than the diameter H. ravenelii 



3 Trichomes 16-19 mic. in diameter; apex of trichome somewhat taper- 



ing, scarcely capitate; cells 2-5 times shorter than the diameter 



H. heterotrichus 



258. Hydrocoleus comoides (Harvey) Gomont. Monogr. Oscill. 73. pi. 

 12. f. 3-5. 1893. De Toni. Syll. Algar. 5: 315. 1907. 



