OSCILLATOKIACEAE. 621 



3. Oscillatoria Corallinae Gomont, Monogr. 238. pi. 6. f. 21. 1893. 



On Halimeda, etc., Mariguana : Europe ; North America. Type from France. 



4. Oscillatoria tenuis Ag. ex Gomont, Monogr. 241. 1893. 



Watl ing's Island : of world-wide distribution, fresh water, occasionally sub- 

 marine. Type from Sweden. 



2. TRICHODESMIUM Ehrenb. Ann. Phys. u. Chem. 18: 506. 1S30. 

 1. Trichodesmium Thiebautii Gomont, Jour. <le Bot. 4: 356. 1890. 



Pelagic in Gulf Stream, between Gun Cay and Florida : Bermuda : Guadeloupe 

 and Canary Islands. Type from Guadeloupe. 



3. PHORMIDITJM Kiitz. ex Gomont, Monogr. 176. 1893. 



Trichomes distinctly torulose, 1. 2-2.3 in diameter. 1. P. fragile. 



Trichomes not torulose. 



Trichomes less than 2 /t in diameter ; forming definite carti- 

 laginous discs or cushions. 2. P. Hendersonii. 

 Trichomes 2, in diameter or more. 



Trichomes 2-2.5 w in diameter, cells 1.5-3 diameters long. 3. P.ralderiamtm. 

 Trichomes over 3 in diameter. 



Apical cell obtusely conical, trichomes 3-4. 5 in di- 

 ameter. 4. P. Coritim. 

 Apical cell truncate, cells 5 in diameter or more. 

 Cells usually shorter than their diameter, dissepi- 

 ments often constricted, sheaths loose and dif- 

 fluent. 5. P. Retztt. 

 Cells usually longer than their diameter, trichomes 



always cylindrical, sheath close, persistent. 6. P. ptilvinatum. 



1. Phormidium fragile Gomont, Monogr. 183. pi. 4. f. 13-15. 1893. 



On walls of fresh-water tanks, New Providence : Europe ; Africa ; North Amer- 

 ica. Type from Italy. 



2. Phormidium Hendersonii M. A. Howe, Smiths. Misc. Coll. 68": 3. 1918. 



Forming definite discs or cushions on rocks, Watling's Island : Cuba, Porto 

 Rico. Type from Cuba. 



3. Phormidium valderianum Gomont, Monogr. 197. pi. 4. f. 20. 1893. 



Among other algae, New Providence, North Cat Cay, Watling's Island : Europe ; 

 North America ; fresh water and marine. Type from Italy. 



4. Phormidium Corium Gomont, Monogr. 192. pi. 5. f. 1-2. 1893. 



Great Ragged Island : generally distributed. Type from Sweden. 



5. Phormidium Ketzii Gomont, Monogr. 195. pi. 5. f. 6-9. 1893. 



Caicos Islands : generally distributed. Type from Sweden. 



6. Phormidium pulvinatum Collins, sp. nov. 



Marinum. Strato pallide aerugineo, erasso, compaeto, pulvinato; filam- 

 entis rectis vel leviter curvatis, vaginis tenuibus, membranaceis, persistentibus, 

 adhaerentibus nee diffluentibus ; trichomatibus pallide aerugineis, cylindrieis, 

 apice rectis, non capitatis nee attenuatis ; cellnlis 7-9 /j. diam., tj-l$ diam. 

 longis; dissepimentis non granulatis; eellula apicali rotundata. 



Stratum pale aernginous, thick, compact, pulvinate ; filaments straight or 

 slightly curved; sheaths thin, membranaceous, persistent, adherent but not 

 diffluent; triehomes pale aeruginous, cylindrical, apex not attenuate nor capi- 

 tate, 7-9 n in diameter, cells f-14 diameters long, dissepiments not granulate; 

 apical eel] rounded. 



