l8 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



SUB-FAMILY I. LYNGBYE.E. 



In this sub-family there is never more than one trichome 

 in a sheath, and the sheath may be thick or thin, or even 

 wanting. In some genera the trichomes are twisted. The 

 cells may be of varying thickness and length, but usually the 

 thicker the trichome the shorter the cell. Oscillatoria, Phor- 

 midium, and Spirulina exhibit a rotary or gliding motion. 



Key to Genera. 



1. Trichomes consisting of many cells 2 



Trichomes consisting of one cell, spirally twisted. . . . 



Spirulina* 



2. Filaments simple, or falsely branched ; sheaths firm ; 



apices of filament straight 3 



Filaments simple ; sheaths thin, always hyaline, 

 mucous, and more or less readily fusing together; 

 apices of trichomes straight ; oscillating or rotary 

 motion evident 4 



3. Filaments free, or forming felt-like masses; pseudo- 



branches present, often in pairs Plectonema* 



Filaments forming er^ct tufts; pseudo-branches often 



present and solitary Symploca 



Filaments free and unbranched ; free-floating, or 



forming a matted stratum Lyngbya* 



4. Filaments more or less agglutinated by their mucous 



sheaths ; cells of filaments often slightly separated 



by a thin mucous layer iPhormidium* 



Filaments destitute of sheaths ; free, straight or with 



curved extremities Oscillatoria* 



Filaments destitute of sheaths ; twisted into a regular 



spiral , Arthrospira* 



Description of Genera. 



Spirulina Turp. Filaments unicellular, more or less 

 motile, spirally twisted, usually surrounded by a colorless, 

 somewhat liquid mucilage. 



S. tenuissima Kutz., Fig. 291. 



