rarely slightly curved; cells equal in length to the diameter, after division 

 shorter; transverse walls very distinctly granulated; cell contents finely 

 granular, pale olive, 



United States. (Bailey). Maine. (West). Massachusetts. Newton. 

 (Farlow). Maiden. (Collins). Rhode Island. Common. (Bennett). New 

 Jersey. Frequent in wet places. (Wolle). Iowa. Usually floating free 

 in stagnant water. Iowa City. (Hobby). Ames. (Bessey, Buchanan). 

 California. On moist cliffs above high tide. Common. (Anderson). 



143. Oscillatoria tenuis Agardh. Algarum. Decades. 2: 25. 1813. Gomont. 

 Monogr. Oscill. 240. pi. 7. f. 23. 1893. De Toni. Syll. Algar. 5: 

 166. 1907. 



Maze and Schramm. Essai Class. Algues Guadeloupe. 16. 1870-77. 

 Rabenhorst. Algen Europa's. no. 2536. 1878. (O. cortiana). Dickie. 

 On the Algae found during the Arctic Expedition. Journ. Linn. Soc. Bot. 

 17: 8. 1880. Farlow. Notes on the Cryptogamic Flora of the White 

 Mountains. Appalachia. 3. 236. 1883. Wolle. Fresh-Water Algae U. S. 

 313. pi. 206. f. 14. 1887. Bennett. Plants of Rhode Island. 115. 1888. Col- 

 lins. Algae of Middlesex County, Massachusetts. 15. 1888. (O. viridis). 

 Wolle and Martindale. Algae. Britton's Catalogue of Plants found in New 

 Jersey. Geol. Surv. N. J. 2: 609. 1889. Rosenvinge. Les Algues Marines 

 du Greenland. Ann. Sci. Nat. Bot. VII. 19: 162. 1894. Tilden. American 

 Algae. Cent. I. no. 75. 1894. Saunders. Protophyta-Phycophyta. Flora of 

 Nebraska. 21. pi. i. f. 16. 1894. Tilden. List of Fresh-water Algae col- 

 lected in Minnesota during 1894. Minn. Bot. Studies, i: 235. 1895. Collins, 

 Holden and Setchell. Phyc. Bor.-Am. Fasc. 3. no. 102. 1895. Tilden, 

 American Algae. Cent. II. no. 190. 1896. Collins. Algae. Flora of the 

 Blue Hills, Middlesex Fells, Stony Brook and Beaver Brook Reservations 

 of the Metropolitan Park Commission, Massachusetts. 127. 1896. Rosen- 

 vinge. Deuxieme Memoire sur les Algues Marines du Greenland. Medd. 

 om Greenland. 20: 121. 1898. Tilden. List of Fresh-water Algae col- 

 lected in Minnesota during 1896 and 1897. Minn. Bet. Studies. 2: 29. 1898. 

 Observations on some West American Thermal Algae. Bot. Gaz. 15: 101. 

 pi. 9. f. 20. 1898. Collins. Preliminary Lists of New England Plants, — 

 V. Marine Algae. Rhodora. 2: 42. 1900; The Algae of Jamaica. Proc. Am. 

 Acad. Arts Sci. 37: 239. 1901. Snow. The Plankton Algae of Lake Erie. 

 U. S. Fish Comm. Bull, for 1902. 22: 393. 1903. Setchell and Gardner. 

 Algae of Northwestern America. Univ. Calif. Pub. Bot. i: 183. 1903. 

 Collins. Phycological Notes of the late Isaac Holden. — II. Rhodora. 7: 

 236. 1905. Borgesen and Jonsson. The distribution of the Marine Algae 

 of the Arctic Sea and of the Northernmost Part of the Atlantic. Botany of 

 the Faeroes. Appendix. XXV. 1905. Brown. Algal periodicity in cer- 

 tain ponds and streams. Bull. Torr. Bot. Club. 35= 242, 247- 1908. Bu- 

 chanan. Notes on the Algae of Iowa. Proc. Iowa Acad. Sci. 14: 14. 1908. 



Plate IV. fig. 17, 18. 

 tiant mass thin, bright, rarely dull blue-green; trichomes 4-10 mic. in 

 diameter, straight, fragile, usually slightly constricted at joints; apex of 

 trichome straight or curved, neither tapering nor capitate; apical cell con- 

 vex, showing a slightly thickened outer wall; cells 2.6-S mic. in length; 



