624 SCYTONEMATACEAE. 



2. Schizothrix chalybea Gomont, Monogr. 57. pi. 9. f. 3-5. 1893. 



On mud, in company with Scytonema velutinum, New Providence. Type locality 

 Mexico ; no other records. The determination is from the description, as type ma- 

 terial is at present inaccessible. 



-N 



Family 4. NOSTOCACEAE. 



1. NOSTOC Vaucher, ex Born. & Flah. Ann. Sci. Nat. Bot. VII. 7: 181. 1888. 



1. Nostoc commune Vaucher, ex Born. & Flah. Ann. Sci. Nat. Bot. VII. 7: 



203. 1888. 



New Providence, Castle Island, and Crooked Island : universally distributed in 

 warm and temperate regions, on ground and rocks. Type from Switzerland. 



2. HORMOTHAMNION Grunow, ex Born. & Flah. Ann. Sci. Nat. Bot. VII. 



7: 259. 1888. 



1. Hormothamnion enteromorphoides Grunow, ex Born. & Flah. loc. cit. 260. 



1888. 



North Cat Cay, Caicos Islands, and Watling's Island : generally distributed in 

 tropical and subtropical waters. Type from Guadeloupe. 



Family 5. SCYTONEMATACEAE. 



1. SCYTONEMA Ag. ex Born. & Flah. Ann. Sci. Nat. Bot. VII. 5: 



85. 1887. 



1. Sheaths homogeneous or with uniform parallel strata. 2. 



1. Sheaths with plainly divergent strata. 5. 



2. Aquatic ; sheaths firmly membranaceous. 1. $. cincinnatum. 



2. Terrestrial. 3. 



3. Heterocysts compressed, shorter than the diameter of the tri- 



chome. 2. S. Millei. 

 3. Heterocysts quadrate or longer. 4. 



4. Filaments mostly prostrate, 10-18 ^ in diameter. 3. S. ocellatum. 



4. Filaments in erect fascicles, usually 7-12/u, in diameter. 4. S. Hofmanni. 



5. Strata of sheath moderately divergent, rather firm. 5. $. myochrous. 

 5. Strata of sheath strongly divergent, gelatinous and diffluent. 6. 



6. Cells and heterocysts shorter than the diameter of filament. 6. 8. velutinum. 



6. Cells quadrate or longer ; heterocysts quadrate or globose. 7. S. crassum. 



1. Scytonema cincinnatum Thuret, ex Born. & Flah. Ann. Sci. Bot. VII. 5: 



89. 1887. 



New Providence and Bimini : widely distributed. Type from Germany. 



2. Scytonema Millei Born. & Flah. Ann. Sci. Nat. Bot. VII. 5 : 93. 1887. 



New Providence, Berry Islands, South Cat Cay, and Watling's Island: North 

 and South America. Type from Guiana. 



3. Scytonema ocellatum Lyngb. ex Born. & Flah. Ann. Sci. Nat. Bot. VII. 5: 



95. 1887. 



New Providence : widely distributed. Type from Denmark. 

 / 



4. Scytonema Hofmanni Ag. ex Born. & Flah. Ann. Sci. Nat. Bot. VII. 5: 



97. 1887. 



New Providence, Abaco, and Acklin Island : widely distributed. Type from 

 Sweden. 



