Tilden: LIST OF FRESH-WATER ALGAE. 29 



263. Oscillatoria tenuis AGARDH. Alg. Dec. 2 125. 1813. 

 With no. 261. 



264. Gloeocapsa calcarea n. sp. 



Forming a calcareous crust, light gray to light aerugi- 

 nous in color, 2-3 mm. in thickness ; cells 6-9 mic. 

 in diameter, 4-16 united in families ; families 25-50 

 mic. in diameter ; sheath colorless, somewhat thin ; 

 cell-contents aeruginous, granular. 



Associated with several other lime-secreting algal forms. 



On boards where spring water from trough drips down 

 constantly. Osceola, Wisconsin. September 15, 1897. 



